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According to William Adama, her marriage to Saul Tigh was the reason that he took to drinking. While her husband was away from home, she apparently "went through half the (Colonial) fleet" in her sexual promiscuity. During the occupation of New Caprica, she collaborated with the Cylons and was killed by her husband, only to download to a Cylon Resurrection Ship (No Exit). Besides Anders who regained his memories due to a bullet to the brain, Ellen was the only one of the Final Five to ever regain her full memories which was due to her resurrection after Saul poisoned her to death in her old body.
2,000 Years Ago
Ellen Tigh lived on Earth two millennia ago. Like all humanoids living on Earth at the time, she was a Cylon: a member of the Thirteenth Tribe. There, she was one of five scientists researching "organic memory transfer", a technology which had originated on Kobol, but fell out of use on Earth once the Thirteenth Tribe Cylons started to procreate naturally. Galen Tyrol did a lot to resurrect the technology, but it was Ellen who made the final advance that brought it back online. She was trapped under rubble in the lobby of her apartment building when nuclear war began. Her husband and fellow researcher, Saul, heard her cries and was able to clear only superficial debris from around her before they were both killed by the subsequent blasts. Her dying words to Saul were, "Saul, it's okay. Everything's in place. We'll be reborn…again. Together." (Sometimes a Great Notion, No Exit) They and the other members of the Final Five downloaded into new bodies on a ship they'd placed in orbit. Knowing that humanity would continue to create artificial life, they made their way the Twelve Colonies to warn them about the dangers of doing that, but it took them 2,000 years to get there due to their ship's lack of a jump drive. Travelling at relativistic speeds, they subjectively experienced much less time than that.
Upon their arrival, the first Cylon War was already in progress between humans and Centurions. Ellen and the others made a deal with the Centurions: end the war and the Final Five would help them build humanoid Cylons. They made eight models and their technology was stored in The Colony. The first creation was Number One, better known as Cavil, who was made in the image of Ellen's father John and named after him. Ellen was close to Number Seven but when Cavil got jealous, he wiped out the Number Seven copies permanently, before they could be grown to maturity. Cavil suffocated the Final Five, boxed them temporarily, then eventually unboxed them, downloading them into new bodies but blocking their real memories and implanting false ones then putting them into the human population in order to show them the evils of humanity.
She was unboxed not long after her husband and even though their true memories were gone, they ended up together again and got married. According to a comment made by Cavil, she was unboxed for at least 30 years before the attacks happened. At some point prior to Adama taking command of Galactica she celebrates what seems to be the end of Adama and Tigh's military carrer with them at a bar and is happy that Saul will be home more as she just wants to be with him. However he follows Adama into his command of Galactica and this may have contributed to their estrangment.
Colonel Saul Tigh, estranged from his wife and realizing her tendencies, finds himself burning a cigar hole in a photo of Ellen, just as action station klaxons ring throughout the decommissioned battlestar as the start of the Cylon attack.
With the Colonies destroyed, billions of people are dead and Ellen Tigh is presumed to be one of the many suffering that fate (Miniseries).
During the attacks, she was on Picon in a bar and was chatting with a "mysterious stranger" (in reality a Cavil who wanted to see if she'd learned her lesson) and revealed that she hadn't changed. Picon was hit by nukes, and the bar was destroyed while Ellen and Cavil huddled together. Ellen survived the blast and destruction but was severely hurt. Cavil, who emerged pretty much unscathed, saved her as he felt she hadn't learned her lesson yet and needed to be alive longer to learn it. He helped her onto a Raptor and went with her to the Rising Star, where he spoke with her about the attack and the Five, but she kept drifting in and out of consciousness (still being seriously injured) and apparently either didn't hear or register what he said (The Plan).
Character History at a Glance
One year after New Caprica is colonized, Ellen Tigh settles on the planet. Her husband joins her later, after Admiral Adama's insistence. Interestingly, they seem to fully reconcile during this time (possibly due to Saul leaving the Colonial Fleet which is something she always wanted so she could be with him full time). When the Tighs encounter Starbuck, both greet her warmly having apparently put aside their differences with her at some point. Shortly thereafter the Cylon fleet discovers the planet, the Colonial Fleet in orbit jumps away, and the Cylon occupation of New Caprica begins (Lay Down Your Burdens, Part II).
Four months after the occupation, Ellen Tigh's husband is imprisoned in the New Caprica Detention Center, resulting in the loss of his right eye. In order to secure his release, Ellen enters into a deal with a Cavil model. After her sexual encounter with Cavil, her husband is released (Occupation).
However, as Ellen Tigh later finds out from this same Cavil, Saul is released in order to further the Cylons' plans to tighten their grip on the civilian population. Despite the release, Ellen reports back to Cavil to further fornicate with him, suggesting some sort of long term sexual agreement. In the aftermath of a session, Cavil demands that she must find out when the next high-level meeting of the resistance is to convene; failure to do so will result in Saul being recaptured and imprisoned again.
The map is later found on a dead humanoid Cylon by Anders' team after he and Fleet liaison Sharon Agathon eliminate the Centurion attack. Ellen Tigh is soon found and forced into the underground hideout, where Colonel Tigh is told of his wife's deception and confronts his wife (Exodus, Part I).
The resistance leaders compel Saul Tigh to execute his wife for collaboration with the Cylons. Saul carries out the execution by poisoning Ellen's drink prior to the Battle of New Caprica (Exodus, Part II).
Saul's Vision of Ellen
When Colonel Saul Tigh visits Caprica Six in the brig, to inform her that her request to see Hera Agathon has been denied, he begins to see Ellen in Six's place. The woman he sees still has the clothes and hair of Number Six, but the face and body of Ellen Tigh. She speaks the same words as Six, but in Ellen's voice.
Later, Colonel Tigh returns to the cell where Caprica Six is held. Wanting to find out how Cylons deal with pain and guilt, he questions Six to learn that the Cylons have modeled their brains around the human brain and have found a "human" way to shut off pain by accepting it. During this conversation, she removes Saul's eye patch in an act of tenderness, which Saul rebukes (Escape Velocity). However, their relationship soon becomes sexual and Tigh, still occasionally seeing Ellen in Caprica's place, impregnates the Cylon ("Sine Qua Non").
Revelation of her true nature
In a vision on Earth, Saul Tigh sees Ellen trapped underneath a slab of rock fallen after a nuclear blast. He tries to free her, but before they're both killed in another nuclear blast she tells him that they'll be reborn together. Coming out of the vision, Saul Tigh realizes the truth: Ellen is the last of the Final Five.
Post-New Caprica Resurrection
After dying on New Caprica, Ellen downloads into a new body aboard a Resurrection Ship. Initially frightened, Ellen quickly remembers her entire history, including her time on Earth, her resurrection having apparently restored all of her memories. She is soon confronted by Brother Cavil, who she calls "John." It is revealed that John was the first humanoid Cylon designed by the Final Five. It soon becomes evident that all of the seven familiar humanoid Cylons were designed by the Final Five, as well as an eighth model, Number Seven, whose line was destroyed by Cavil.
Ellen is held prisoner on a basestar for 18 months, and allowed contact only with Cavil and Boomer. After the destruction of the Resurrection Hub, Cavil threatens Ellen with vivisection unless she helps the Cylons rebuild the hub. Ellen refuses, and is soon being readied for surgery, when Boomer helps her to escape (No Exit). Ellen and Boomer make it back to the Galactica (Deadlock). She is seen discussing the mission to The Colony with Tory Foster, and volunteers the Final Five to go, much to Tory's dismay (Daybreak, Part I).
During the battle, she Tory and Tyrol take care of Anders and Ellen stays by his side during everything. She is shocked to learn that Tory murdered Cally, but both she and Tigh forgive Tyrol for killing her in revenge. She and Saul rekindle their relationship and decide to spend the rest of their lives together on humanity's new homeworld which they name Earth (Daybreak, Part II).
In the DVD commentary for the Miniseries, it is revealed that Ellen Tigh was originally portrayed in picture form only by executive producer David Eick's wife, Jennifer. The picture was later replicated for the series with Kate Vernon taking the place of Mrs. Eick and the scene reshot, so Saul Tigh is seen burning a picture of Vernon in the "flashback" sequence at the beginning of "Tigh Me Up, Tigh Me Down."
The Macbeth Connection
Ellen Tigh can be profitably compared with one of Shakespeare's most memorable women. Like Lady Macbeth, Ellen is married to a man who is in the line of command, but who doesn't want the top job. She uses a combination of insult, flattery, and sexual temptation to get her husband in the game, arranges the murder of others, and even makes alcohol one of her most potent weapons (in the play, Lady Macbeth gets the castle guards drunk so that she and her husband can kill the king and princes). In the words of Lady M herself, to her husband, "Hie thee hither, that I may pour my spirits in thine ear, and chastise with the valour of my tongue all that impedes thee from the golden round."
In fact, of all Shakespeare's plays, Macbeth is a particularly appropriate one for a series about evil robots who seem human on the outside ("fair is foul and foul is fair"), who are experts at lying and manipulation ("And oftentimes, to win us to our harm, the instruments of darkness tell us truths, win us with honest trifles, to betray us'n deepest consequence"), and who chase our heroes through the gulf of space (at least one scholar has noted that all of the play's most memorable scenes "take place either at night or in some dark spot"). Like Macbeth himself, Saul Tigh is famous for a bout of vicious hand to hand fighting in the recent war ("For brave Macbeth ... disdaining Fortune, with his brandish'd steel which smok'd with bloody execution ... carv'd out that passage").