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Human Name

Simon O'Neill
Birth place {{{birthplace}}}
Birth Name
Birth Date {{{birthdate}}}
Nickname {{{nickname}}}
Introduced The Farm
Death Airlocking, shooting and destruction of The Colony
Marital Status One copy is married to Giana O'Neill
Family Tree View
Role Cylon doctor / scientist,
fleet medic,
Caprica Buccaneers team doctor
Serial Number {{{serial}}}
Portrayed by Rick Worthy
Four is a Cylon
Four is a Final Five Cylon
Four is a Human/Cylon Hybrid
Four is an Original Series Cylon
Related Media
@ BW Media
Additional Information

"Number Four"[1], also referred to by his human name Simon O'Neill, is a humanoid Cylon that speaks calmly and purposefully, and tends to use logic as a means for his operation or resolving issues (TRS: "Torn"), and is not as religious as his counterparts.[2] This model appears to be the medical specialist of the Cylons and also takes on the role of a doctor or medic when functioning as an infiltrator (TRS: "The Farm", "Six of One", "The Plan"). Apparently the infiltrators of this type are more likely to use their medical skills subversively than to engage in direct combat.

Known Pre-Cylon Civil War Copies

Dr. Simon

One copy of this model, calling himself "Simon," cares for Kara Thrace as a medical doctor after she is shot in a Cylon ambush. Simon tries to casually persuade Thrace into bearing children but is unsuccessful. When his diplomatic efforts fail, he surgically explores her ovaries without Thrace's permission, either partially removing an ovary or its eggs. On orders from a copy of Number Six, Four arranges a time to surgically remove Thrace's ovaries. Before Simon can sedate her again and remove her ovaries, Thrace's suspicion that he is a Cylon is confirmed. In conversation he uses her call sign, which she never mentioned in his presence. Thrace kills him and escapes from the farm. Moments later, another copy intercepts Thrace just as she exits the building reaches the outside of the compound. Before he can speak further, members of the Resistance immediately kill him as they storm the farm to liberate Thrace (TRS: "The Farm").

Simon O'Neill

One copy infiltrates the human Fleet as a married man and has a step-daughter. He is very reluctant to harm the humans as he is now sympathetic to them. He truly loves his family and has trouble carrying out Cavil's orders to blow up the ship he lives on. He freaks out his wife Giana O'Neill who temporarily leaves him and he then agrees to carry out Cavil's order if his family is spared, but Cavil refuses. After one final sexual encounter with his wife, he kills himself by airlocking himself after leaving a suicide note, not wanting to betray his family. He does this while outside of resurrection range and his death is thus final.

Giana later learns the truth about him when Kara Thrace returns to the Fleet with information about his model, and Giana sees the picture of another copy in an old newspaper article. Galen Tyrol comforts her by correctly pointing out that Simon killed himself rather than doing anything against the Fleet (TRS: "The Plan").

C-Bucs Four

Yet another copy is the doctor of the Caprica Buccaneers. He is well aware of his identity as a Cylon, but he is unaware of the true nature of Samuel Anders and thus is puzzled by Cavil's interest in Anders. He does his part to undermine the resistance by giving too much morpha out and contaminating anti-radiation meds, but is unable to do anything against the Resistance without compromising his cover as their doctor. When Kara Thrace and Karl Agathon show up, he hides himself from them in fear that they will recognize him as a Cylon and apparently arranges to have Thrace sent to a farm. He gets frustrated with the Cavil copy that joins them as Cavil won't reveal their location to the Cylons, wanting to hear Anders' confession (in reality wanting to see if he learned his "lesson"). This copy of Simon is exposed when the resistance kill another copy during Kara Thrace's rescue and recognize him as identical to their Simon. Anders sends Jean Barolay back to kill him (TRS: "The Plan")[3].

Infected Four

A Four captured on an infected basestar near the Lion's Head Nebula is interrogated on Galactica. He reveals information about the ship and the Cylons' motives for abandoning it, in exchange for a cure promised by the humans. However, there is no cure, only a treatment. This Four is permanently killed when Karl Agathon sabotages the environmental control system, killing the Cylon prisoners to stop them from being used as biological weapons (TRS: "A Measure of Salvation").

Other Copies

Number Four on New Caprica
At least one other copy operates on Cylon-occupied Caprica (TRS: "Downloaded"). A Four is present in President Baltar's office during the Battle of New Caprica (TRS: "Exodus, Part II").

One Four, assigned as part of one basestar's command crew that witnesses a sister basestar's plight, determines that a decision to rescue the infected basestar cannot be reached scientifically (TRS: "Torn").

Known Cylon Civil War Copies

A Four performs a lobotomy on a Raider, which this model votes for. At least two of these models are slain by Centurions, along with two Fives and a One (TRS: "Six of One"). The Fours fall under Cavil's banner in the Cylon Civil War. A team of Fours on board Cavil's Basestar were prepared to operate on Ellen Tigh's brain to learn the secrets of resurrection (mentioned but not seen, "No Exit"). Later, a copy is shown aboard The Colony preparing the examination of Hera (TRS: "Daybreak, Part I").

A copy, possibly the same one, is killed by Boomer when she rescues Hera. Several Number Fours are among the boarding party led by John Cavil that storms Galactica during the assault on The Colony. One assaults the CIC directly with Cavil and a Five. The Four is mortally wounded, possibly by Admiral William Adama and is left standing gasping for breath before Adama kicks him down. After a tenuous truce is declared, one Four oversees the transfer of resurrection data from the Final Five to the Colony Hybrids, but when the truce is broken when Galen Tyrol kills Tory Foster the Four in the CIC quickly opens fire with another Five. He is quickly killed by Kara Thrace. The remaining Fours aboard the Colony all perish when it falls into the naked singularity it was orbiting and is obliterated (TRS: "Daybreak, Part II").


  • Actor Rick Worthy does not film any new scenes for "Downloaded" and is thus uncredited: briefly during the cafe scene, we see another bald black man from behind, and we see him walking by in some of the outdoor scenes in the background. It is clearly implied to be Simon, however he is not credited and RDM stated in the podcast that it was just an extra standing in for him.
  • Simon was the first new humanoid Cylon model revealed after the Miniseries, and then brought the then-total number of known models to five. Although nine models had actually been seen onscreen at this point, Saul Tigh, Galen Tyrol, Ellen Tigh and Samuel Anders had not yet been revealed as Cylons.


  1. This number is revealed in the episode "Six of One".
  2. Craddock, Linda (27 November 2006). The Scifi World: Rick Worthy interview (backup available on (in ). Retrieved on 19 February 2007.
  3. In a deleted scene, this copy contaminates the resistance group's anti-radiation medication before he is killed.

Season Four
Season Four
A season of the Re-imagined Series
Discuss this season at the Battlestar Forum
Number of Episodes 22 (list)
Executive Producer(s) Ronald D. Moore
David Eick
US airdates USA 2007-11-24 (Razor)
2008-04-04 (Season 4.0)
2009 (Season 4.5)
CAN airdates CAN 2007-11-24 (Razor)
2008-04-04 (Season 4.0)
2009 (Season 4.5)
UK airdates UK 2007-12-18 (Razor)
2008-04-15 (Season 4.0)
2009 (Season 4.5)
DVD release USA USA 2007-12-04 (Razor)
USA USA 2009-01-06 (Season 4.0)
USA USA 2009-07-28 (Season 4.5)
UK UK 2007-12-26 (Razor)
UK UK TBA (Season 4.0)
Starting Population 41,399 survivors
Ending Population ~38,000 survivors
Extended Info Final season of the Re-imagined Series. Features "Razor" as episodes 1 and 2, as well as two webisode series, the "Razor Flashbacks" and "Face of the Enemy".
Season Chronology
Previous Next
Season 3 (2006-07) Four (Final Season)
Related Information
Official Summaries
R&D SkitsView
Podcasts - Audio
IMDb entry
Promotional Material
Razor Flashbacks
Online Purchasing
Available at's Unbox – [ Purchase]


The final season of the Re-imagined Series, surrounding the revelation of the last member of the Final Five, the mystery surrounding Kara Thrace's return, the continuing search for Earth that will likely end in her discovery by the Fleet, and a cult lead by the well-loathed, unwanted (yet pardoned) disgraced former president, Gaius Baltar.



  • A two hour television movie called "Razor," set during the events of Season 2, aired on November 24, 2007. It contains a framing story about Lee Adama's first mission as commander of Pegasus, but flashes back to a time prior to "Pegasus" during Helena Cain's command, as well as to the Cylon War.
  • The Fleet finds Earth in "Revelations," only to find that the planet was devastated in a nuclear event.
  • In an Entertainment Weekly interview , Ron Moore reveals who is not the fifth Cylon. According to the article, neither William Adama, Lee Adama, Laura Roslin, Kara Thrace, Karl Agathon, nor Gaius Baltar is the fifth Cylon. However, some controversy about the related photo exists, where fans were looking for significant, hidden clues in the same vein as "The Last Supper" photo depicting Jesus and the Apostles. In reaction to this, Aaron Douglas (Galen Tyrol) discredited aspects the "Last Supper" mirroring of the image. See The Last Supper for more information.

Character developments

  • Katee Sackhoff is back as Kara Thrace. Despite suspicions against her from many sides, thinking she may be a Cylon, she is given command of the Demetrius in an attempt to find Earth.
  • The third, "The Ties That Bind," features the death of another well-established character.
  • Lee Adama continues to be a civilian. He officially retires from the Colonial Fleet and first becomes a politician by taking the Caprica's seat on the Quorum of Twelve, before being sworn in as interim President of the Colonies in Laura Roslin's absence.
  • Mark Sheppard reprises his role as Romo Lampkin in "Sine Qua Non" and will appear again in one episode later in the season [1].
  • Nana Visitor, known to genre viewers as Kira Nerys on Star Trek: Deep Space Nine, appears in the episode "Faith". She plays a cancer patient named Emily Kowalski who meets Laura Roslin in Galactica's sickbay. The two bond and eventually discuss matters of morality and faith. All of Visitor's scenes are with Mary McDonnell.
  • Taylor assured fans that the romantic polygon between Lee Adama-Anastasia Dualla-Kara Thrace-Samuel Anders was "pretty thoroughly" put to bed in Season 3 and will not be revisited again.[2]
  • As for Dualla, Taylor claimed that: "I think Dee is someone who wears more of her character on the surface. She’s basically a pretty straightforward, upbeat character, someone who says what’s on her mind and is honest about what she’s feeling. And maybe in the context of the show that makes her a bit less dark and tortured, and perhaps less compelling, than a character such as, say, her romantic nemesis in said polygon: Kara. However, I think we may find that even a personality such as Dee’s has its dark side. ‘Nuff said for now."[2]
  • Jamie Bamber apparently slipped on the fact that Thrace's and Leoben Conoy's scenes in "Sometimes a Great Notion," which are apparently set in a forest, are set on Earth.[3]
  • The three women who took Baltar in the season 3 finale belong to a monothestic cult, a portion of Colonials who have come to believe in a single Cylons God. They look to Baltar as their leader, a task he is reluctant to take, but, as Moore notes, "at what point does he start to believe the message?"[4]

Cylon developments

  • Moore indicated that the last of the Final Five will be revealed this season.[5]
  • A civil war breaks out among two factions of the humanoid Cylons over a disagreement on how to deal with disobedient Raiders, the Final Five and the boxed Threes. The rebels faction is led by an assertive variant of Number Six known as Natalie, who restores the Centurions' sentience and allies itself with the Colonials. The other faction is led by Cavil and Boomer. The conflict results in the destruction of the Cylons' central downloading facility, making them completely mortal. Ron Moore adds that the Cylons and humanity will "grow toward a common understanding."[4]
  • Number Three, played by Lucy Lawless, is unboxed in the episode "The Hub". She subsequently assumes a leadership role among the Cylon rebels, and eventually agrees to a truce with the Colonials. Together, the two groups reach Earth.


  • Moore indicates that this season begins the "third act in the three-act structure where we're all moving towards the finale and the climax of all these different plot lines. In my head there's two chapters to go in the story and those can be of varying lengths." [6]
  • On Friday, June 1st 2007 the SciFi Channel issued a statement saying that Season 4 is going to be the final season. Ending the series with the upcoming 22-episode fourth season was a creative decision made by the show's executive producers Ronald D. Moore and David Eick. SciFi executive VP of original programming Mark Stern said the channel's brass "respect the producers' decision to end the series." [7]
  • Production of Season 4 was preempted by the 2007-2008 Writers Strike, which forced production to shut down after production of the episode "Sometimes a Great Notion". Production resumed on Season 4 following the conclusion of the strike, but as a result, just as with Season 2, the season was split into two widely-space halves (effectively making Season 4 two separate seasons, with the second half becoming known as Season 4.5). The first half of Season 4 began airing in the spring of 2008; the second half began in January 2009 [8]. The final episode of the series will air in March 2009.
  • A series of 10 webisodes, written by Jane Espenson and Seamus Kevin Fahey and entitled "The Face of the Enemy," were webcast prior to the broadcast of the Season 4.5 premiere episode.[8].
  • Moore made his directorial debut in the second half of this season with episode 12, "A Disquiet Follows My Soul".[9]
  • The final number of survivors that make it to the new Earth, around 38,000, is stated by Bill Adama during the second hour of Daybreak, Part II.




Production Crew


Directors & Writing Staff

To view the list of all the directors and staff, go to the Battlestar Galactica Crew Guide page.


To view the list of episodes, go to the Battlestar Galactica Episode Guide page.

Official Statements

It will be a serialized show to an extent. I think what we talked about with the network — because their concern is the drop-off in viewers and giving too many hurdles for new viewers to overcome to watch the show — we're always going to try to provide at least an episodic quality to each show. Even though there are plotlines that are ongoing over the course of the whole season, we'll try to give you something in each episode that you can hold on to that starts and stops within that episode.[10]
  • Moore discusses the Final Five:
Well, you can see from the end of the third season that they all sort of are still the same people. They're still the same characters. They didn't switch over and become robots suddenly. So essentially you're going to see an extension of that initial moment where they try to figure out what does this mean to them. If they're Cylons, when did that begin? What are their true backstories and what are they meant to do? What are they supposed to do? Are they dangerous to each other? Are they dangerous to the ship? Do they trust any of the people around them? Should they keep the secret only among themselves? That's essentially where their storylines are going to pick up.[11]
  • Moore discusses ending the series:
Yeah, I mean, the burden [in breaking 20 episodes for this season] then became okay, now we have a great deal to wrap up and bring resolution to and we wanted to pay off a lot of things and we wanted to tie up a lot of loose threads. It felt like we had more than enough to get to where we were going to, whereas usually when you're facing the 20 episode order, it's like, "Okay, whew, we need 20 of these? Where are we going to get 20 of these?" You have to start breaking it down into smaller, bite sized chunks and move yourself along. This time, it was almost like, "Okay, let's make sure we've got enough time to get everywhere we need to go."[11]
We will find Earth. And [my character, Kara Thrace is] not a figment of people's imaginations.
  • Sackhoff discusses ending the series:
I'm happy about it. It is a choice that was made by us. The rug was not pulled out from underneath us. We're going out on a high, with our heads held high. We made the choice and we're going to be able to decide our end and our fate, instead of [having to] wrap it up as fast as we possibly can because we've been canceled. And it was a smart thing to go out on a high. And you know, this is my fourth series. I think I've done more television than anyone else on the show, except maybe Eddie [James Olmos], because of Miami Vice. He's right there with me! But I've done shitloads of television, and every single show the rug is pulled from out underneath you, and you're going, "What do I do now?" And this is such a great opportunity to wrap it up, say everything you want to say in your character, and put it to bed.
Brad and I wrote the opening episode of year four and we were up in Vancouver for its pre-production and some of the first few days of filming. The revelation at the end of last season of our four Cylons who didn't know they were Cylons has once again upset all the chess pieces. So the big challenges starting out this season are how do you play those characters going forward and track their emotional development, or unraveling as the case may be, in a way that's organic as well as genuine and not contrived. Also, as most people know, Starbuck reappeared in the final seconds of last year's finale, so there's also the question of how to deal with that character going forward. There are going to be lots of twists and turns this year. You're going to see our characters wrestling with tormenting problems and experiencing, perhaps, some rather jaw-dropping changes and evolutions. All the dynamics that you may have become used to on Galactica ship itself will be in flux and we think, and hope, that's going to be tremendously fun to watch.[12]
  • Lucy Lawless on the cast and crew reaction behind the scenes:
Things seem great actually; far more comfortable than we did on Xena at this stage, but maybe it hasn’t hit them or maybe it’s an easy adjustment because there are so many of them and several of them are working on Bionic Woman. The mood is really great. I’m surprised how comfortable they are. Halfway through the last season of Xena, the cast tended to get snappish with one another, and I think it was just anxiety of not knowing where your mortgage payments were coming from. I think the writers’ strike is probably of more significance at this moment; than the end of the show. I don’t think it’s quite real to them yet.[13]
In Season 4, Battlestar will be the gayest show on television. Forget secret Cylons, all our characters will be revealed to be gay. We will even see gay Centurions and gay daggits. Actually, the daggits will object to the use of that term and will insist on simply being called dogs. And Season 4 will indeed see the return of a favorite dog, though not necessarily a gay dog… but, um, what was the question again?
Oh, right: Will we see more gay folks on Galactica [this] season. Well, to take a more serious tack, I think part of the point about Cain’s and Gina’s relationship is that the fact that they had a same-sex relationship was no big deal. I think we started from the idea of wanting to explore whether Cain’s anger and revulsion at Gina, so evident in her first appearance in Season Two’s “Pegasus,” had a personal component. And the idea that Cain had had an intimate relationship with Gina quickly came to mind. It made Gina’s betrayal that much more devastating for her.[2]
Inevitably it changes the vibe because there's suddenly a horizon you can see, and we all have personal lives, and coming up to Vancouver for some of us is quite a schlep. Knowing it's the last time changes everything, so yea, it's a different deal.
There's also a real peace of mind that comes with the fact that we're gonna get to finish the story—the story's always begged an ending—and we get to give it to you, so there's a lot of excitement and anticipation attached to that.
It feels like every moment that passes is gone forever now, like the last performance of a play on the last start off with your monologue in the first scene and you know when you finish it that's the last time you'll ever do it. There's a nostalgia that goes with every conscious moment.[14]
It’s ugly. It’s not a happy ending. The final season is not a way of resolving anything. Happy would be tying things in a nice bow. There are no bows being tied.[15]


  1. 'Battlestar Galactica's' fourth season, the strike, and directing in space: The scoop from Ron Moore (backup available on (in English).
  2. 2.0 2.1 2.2 Ryan, Maureen (16 November 2007). Answers to your 'Razor' questions and clues about 'Battlestar Galactica's' final season (backup available on (in ). Retrieved on 16 November 2007.
  3. Roadrunner - Newsdump from Burbank convention (backup available on (in ). (19 November 2007). Retrieved on 20 November 2007.
  4. 4.0 4.1 "'BSG' Season 4 Cheat Sheet" Entertainment Weekly #985. April 4, 2008: 31.
  5. Battlestar Galactica: Secrets from the Set (backup available on (in ). (26 March 2007). Retrieved on 4 July 2007.
  6. Jacks, Brian (6 April 2007). MTV Movie News: 'Battlestar Galactica' Producer Talks Movie(s?), Possible Conclusion (backup available on (in ). Retrieved on 8 April 2007.
  7. SciFi Wire: Battlestar Ending Next Season (backup available on (in ). Retrieved on 1 June 2007.
  8. 8.0 8.1 Talking 'Battlestar Galactica's' finale, 'Caprica' and the 'Battlestar' TV movie with Ron Moore (backup available on (in English).
  9. Verheiden, Mark (24 March 2008). Battlestar Rolls On Tuesday... (backup available on (in ). Retrieved on 3 April 2008.
  10. Four-ward, Cylons: RONALD D MOORE (backup available on (in ). Retrieved on 31 May 2007.
  11. 11.0 11.1 Topel, Fred (13 June 2007). Battlestar Galactica: Ronald Moore talks about Earth (backup available on (in ). Retrieved on 15 June 2007.
  12. "Writes of Passage" Cult Times #144. August 26, 2007: 23.
  13. Elliot, Sean (30 October 2007). Lucy Lawless Teases iF Magazine About Her Return to Battlestar Galactica (backup available on (in ). Retrieved on 30 October 2007.
  14. Bensoussan, Jenna (24 November 2007). ACED Magazine: Battlestar Galactica: Cast Interviews (backup available on (in ). Retrieved on 25 November 2007.
  15. Beale, Lewis, "Edward James Olmos wraps up 'Galactica,' does community work", New York Daily News, 17 March 2008. Retrieved on 18 March 2008.

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