Pictured clockwise are members Saul Tigh, Jean Barolay, Kara Thrace, Diana Seelix, and Charlie Connor.
The Circle is the name given to a tribunal secretly authorized by President Tom Zarek. The task of this tribunal is to decide the fate of people implicated as collaborators during the Cylon occupation of New Caprica.
The Circle's initial members include Saul Tigh, Galen Tyrol, Samuel Anders, Diana Seelix, Jean Barolay, and Charlie Connor. After the trials and executions of thirteen suspected collaborators, Anders decides that he is no longer able to handle the emotional burden of deciding the life or death decisions made by the group. He is replaced by his wife, Kara Thrace.
It is an interesting irony that three of the founding members are members of the Final Five Cylons, though they are not aware of it.
The suspect list includes Galactica military personnel James "Jammer" Lyman and Felix Gaeta. The Circle convicts Lyman for perpetrating crimes against humanity and treason and executes him by expulsion through one of Galactica's launch tubes. Gaeta, who had served as a presidential aide to Gaius Baltar on New Caprica is also convicted by the Circle of crimes against humanity. Just before Gaeta is to be executed, Tyrol is able to confirm that it was Gaeta who served as the "inside source" during the occupation of New Caprica, passing top-secret information to the resistance. Tyrol convinces the other members of the Circle to stave the execution and Gaeta is released.
While certainly not the normal manner for the trial (and punishment) of suspected traitors, the Circle does have a legal basis. When Anders drops out, the group needs to find a sixth member. As Col. Tigh mentions, they "are not a death squad. [They] need six members to be legal, as the President ordered." (Some viewers might think that he refers to Laura Roslin, but she has not re-assumed the Presidency yet, and with Baltar with the Cylons, this means Tom Zarek has succeeded to the office.)
Fifty-six other suspected collaborators on the list are not tried. The Circle disbands when newly reinstated President Laura Roslin grants general pardons for all collaborators (Collaborators).