Bennett Halverson
Bennett Halverson, played by Summer Glau, is the programmer at the DC Dollhouse. Even by Topher's standards, she is a genius, which, according to Topher, is saying something. Both Topher and Bennett are impressed by each other, but ultimately Bennett's duplicitous nature came to light.
Evidently Bennett has a history of some kind with Caroline Farrell and she imprints Echo with her own memory of Caroline before letting Echo and Perrin leave with the intention of creating and flipping a sleeper trigger.
More is revealed in Getting Closer and we discover that Bennett is truly human and while she felt betrayed by Caroline, that isn't necessarily exactly the way it happened.
"We literally become what we do, not what we've done, or what we will do. We're best defined by our actions in the moment." (Epitaph Two: Return)
Episodes
Bennett appeared in four episodes of Dollhouse.
2.05 The Public Eye aired December 4, 2009.
United States Senator Daniel Perrin has been trying to bring down the Dollhouse for months, but he has never been a danger - until now, when he comes into possession of a material witness (November). The staff believes his wife is a Sleeper Doll who will kill November. (The Senator is too important to be killed.) The Dollhouse sends Ballard to capture November so she'll be safe. Ballard is armed with a device that will incapacitate any Doll that arrives to take November, but Echo and Perrin are caught in the crossfire. In a shocking twist, Perrin is revealed to be a Doll, and his wife is his handler. Suddenly self-aware, he and Echo try to escape, but are captured by personnel from the D.C. Dollhouse. Echo meets the D.C. Dollhouse programmer, Bennet Halverson (Summer Glau), who tortures her. Adelle and Topher head to D.C.
2.06 The Left Hand aired December 4, 2009.
Bennett reveals that she knew Caroline (Echo's original personality) and Caroline left her for dead in an explosion. She imprints Echo with Bennet's memories of Caroline's betrayal. Ballard is unable to sway November who goes to testify. Meanwhile, Adelle has Topher find a way to gain access to Perrin's brain scans. Topher is in contact with Victor who Topher imprinted as himself for support in LA. Echo escapes with Perrin into the real world determined to bring down Rossum and expose everything. Perrin's handler is dispatched to get them back. Adelle meets with the head of the D.C. Dollhouse (Special Guest Star Ray Wise) who reveals Perrin will have Rossum vindicated at the Senate hearings and attack their competitors so that Rossum will be unopposed. Bennet and Topher adapt Topher's incapacitating device to remotely knock out Dolls based on their unique brain scans. Bennet however remotely triggers Perrin to kill Echo. Topher knocks Bennet out and overrides the programming with help from Victor/Topher, but not until after Perrin kills his handler. Perrin shows up at the hearing late and reveals his wife is dead. He then pronounces Rossum a good corporation who has been set up by their immoral competitors, that there is no Dollhouse, and that November is a disturbed woman who was in a mental institution in Canada. November is then taken to the D.C. Dollhouse and imprinted. Back in LA, Topher reveals that Perrin could never turn against Rossum, it was like hardware in his mind rather than software.
2.11 Getting Closer aired January 8, 2010.
The wedge containing Caroline is missing. Bennett Halverson is kidnapped to aid Topher repairing the wedge containing Caroline's mind, which Alpha damaged, as Caroline knows the secret identity of Rossum's head. November who was placed in the D.C. Dollhouse is brought back with Bennett. A flashback reveals the truth concerning Caroline's role in Bennett's maiming. It is revealed that Boyd now has a romantic relationship with Dr. Saunders (guest star Amy Acker), who returns to the Dollhouse at his request. Dr. Saunders, presumably functioning as a sleeper active under Rossum's control, executes Bennett Halverson before she finishes repairing Caroline's wedge. Topher, who loves Bennett, overcomes shock at her loss to finish repairing Caroline's wedge using techniques he learned from Bennett. Caroline's memories (anticipated throughout the episode) now reveal the identities of Rossum's leaders: the current incarnation of Clyde, and Boyd.
2.13 Epitaph Two: Return aired January 29, 2010.
Bennett appeared briefly in a video lecture viewed by Topher. As he reviewed her lesson, he pressed his fingers against her lips on the screen.
This information has been taken from wikipedia.