Bennett Halverson was the chief programmer for the Washington, D.C. Dollhouse and an intellectual genius who was considered one of Rossum's rising stars. Bennett was also well known for her accomplishments achieving technological feats that no one else thought possible were or able to do themselves, such as repairing damaged imprint wedges without data loss or corruption.
Bennett is notable for being exceptionally smart, even by Topher's standards - he said she was a genius and that if he thinks someone is a genius then "double it". Bennett's technology is superior to Topher's (the distance was painfully obvious when the duo's respective brain scans are put together, although Topher claims this is because Echo's brain scan wasn't meant to be complex), but she seems to have some sort of a schoolgirl crush on him, as she became very nervous and was obviously thrilled to meet him.  
Her mannerisms and speech suggest she is a nihilist and also slightly deranged. She can also be manipulative, playing on Topher's attraction to her. Unlike Topher's, Bennett's office is sparse and neatly organized.
Because she has both genius and beauty, Topher suspected her of being an Active imprinted to replace a real Bennett Halverson, like Claire Saunders, but proved himself wrong when his disruptor device had no effect on her. Bennett was surprised by his suspicion because she didn't consider herself beautiful.
According to Bennett during a casual chat with Caroline Farrell, she was "technically" a genius. Caroline also noted that she was "off-the-chart smart" when she browsed though Bennett's file.
Bennett's assistant is Grace.
Studying at Rossum
Noted by Adelle as "one of Rossum's rising stars", Bennett studied neuroscience at Rossum's campus facility in Tucson, Arizona. Caroline Farrell, acting on information stolen from Rossum, enrolled as a student and befriended Bennett. When Bennett found the stolen file on her, Caroline told her the truth and gained her help.
Bennett and Caroline sneaked into the Rossum lab. Bennett guided Caroline in planting bombs, but when Caroline discovered human test subjects, she tried to stop the bombs. The bombs went off, leaving Bennett trapped under rubble, with her left arm crushed. Caroline tried to help Bennett, but is unable to free her. When Caroline sees that security is coming, she leaves Bennett so that only Caroline will be caught and blamed for the bombing. After this, Bennett lost the use of her left arm, and kept it in a sling.
Working at the D.C. Dollhouse
She eventually became the chief programmer of the Washington DC Dollhouse. Her unstable mind distorted the memory and she believes Caroline betrayed her and left her for dead.
Senator Daniel Perrin (actually an Active modified by Bennett) threatened to expose the Rossum Corporation and the Dollhouse organization with help from Madeline Costley. The L.A. Dollhouse dispatched Echo as a hooker in order to damage Perrin's credibility. However, it was unaware that Perrin was actually working for the D.C. Dollhouse branch.
Cindy Perrin (actually Senator Perrin's handler) captured Daniel Perrin and Echo, and when she brought them to the D.C. Dollhouse, Bennett immediately recognized Echo and called her by her former name. She tortured Echo, then gave Echo a distorted memory imprint of herself in the collapsed building, in which Caroline abandoned Bennett to take the blame.
Bennett met Topher at the D.C. Dollhouse along with Adelle DeWitt. The two Dollhouses planned on capturing Echo and Senator Perrin. Topher was able to trick Bennett into giving him a copy of Senator Perrin's brain scan, which he then sent to his copy (imprinted into Victor) in the L.A. Dollhouse. While Topher worked on a remote disruptor system (the "gun") Bennett worked on the program to be transmitted (the "bullet"). However, instead of wiping or disrupting the two Actives, she transformed Senator Perrin into an assassin who would kill Echo.
Bennett allows Echo to escape, helped by Daniel Perrin, then concocts a cover story supported by her injuries (actually from beating her head against a monitor.) This is part of a plan to get Echo out of the D.C. Dollhouse so that Bennett can remote imprint Daniel as an assassin and kill her. Topher knocked Bennett out and then released Daniel, letting Echo escape.
Senator Perrin had killed his handler while in sleeper assassin mode, but later built-in programming prompted him to discredit Madeline Costley anyway.
At the end of the episode, Bennett was seen imprinting Madeline Costley.
Topher suspected that one of the devices he saw her working on was a component of Rossum's ultimate plan, along with his own remote wipe technology and other devices being worked on by other Dollhouse programmers throughout the world. 
The LA Dollhouse kidnaps her to help Topher rebuild a damaged personality wedge. Bennett reluctantly helps, until Topher tells her the wedge contains Caroline's personality. She punches him and refuses to help. Echo approaches her and promises to help Bennett torture Caroline after getting the desired information.
During the time when she was studying in Tucson Tech, Bennett was portrayed as a total nerd, with poor social skills and was generally awkward in interacting with others. She speaks in a very technical manner, often not recognizing slangs or jokes (for example, in reply to Caroline's assurance that she is going to "turn heads" after her makeover, she said that she would mostly be studying them). Despite having rather good looks, she effectively hampered them by having a poor fashion sense, as well as an indifference to her appearance. Despite her various shortcomings, however, she was clearly nice, friendly and good-natured. 
After the accident that lost her the use of a left arm, however, Bennett was somewhat traumatized and grew distinctly colder. She proceeded to become the Chief Programmer for the D.C. Dollhouse, and handled her job with even more apathy than Topher. She was significantly more shrewd, worldly, sly and manipulative (a contrast to her former self, who is more often known as the "manipulated" rather than the "manipulator"), and was seen to speak of more abstract things (like the "sacred trust" that all who work inside the dollhouse have) than she used to. She has also learnt to be sarcastic, sneering at DeWitt's perceived stupidity of kidnapping her. Despite the change in her personality, however, she was still remarkably pleasant, for example to Grace, to whom she offered advice about how to deal with higher ranking people.   
She reserved her warmest side to Topher, for whom she has romantic feelings, and her darkest side to Caroline, whom she sincerely hated for her betrayal. When meeting with Topher for the first time, she went distinctly shy and lost her previous eloquence displayed when interacting with Grace, and she was significantly more tender towards Topher than towards any other individual she has as of yet interacted with. This contrasts starkly with her feelings towards Caroline, at whose mention she seethes with anger. She probably feels that had Caroline not gotten curious and went to investigate the mysterious room in the Rossum building, she would have been able to get out of the lab before the bombs went off. As such, she was not seen to have forgiven Caroline in any way, and displayed her manipulative and malevolent side when attempting to imprint Daniel Perrin to kill Echo.  
The one remarkable trait she kept whether before or after the accident is that she is somewhat brave and not easily intimidated. When she was still studying at Tucson Tech, when confronting a girl who was still taking up a seat in the cafeteria when her lunch is already finished, she proceeded to reason with the girl, being all the time adamant that the girl should vacate the seat. When she learnt that the wedge she was repairing holds Caroline, her most bitter enemy, she also unyieldingly refused to help, despite being locked up. 
- There are several possible references and in-jokes about the television series Firefly, which is also written by Joss Whedon and in which one of Summer Glau's most prominent characters in her career, River Tam, appears as one of the main characters.
- During a flashback of Caroline seeing a picture of Bennett Halverson, she mutters "bet you could kill me with your brain". This is a reference to a casual remark by River, "Also, I can kill you with my brain."
- Bennett's death, being shot through the brain, could probably be another reference to the Firefly series, as in the film sequel to Firefly, Serenity, River pleaded her brother, Simon Tam, to "put a bullet to her brainpan".
- During the flashback when Caroline was helping Bennett with a make-over, Bennett commented on how fearless she perceived Caroline to be, and said that she would like to examine Caroline's amygdala. In Firefly, River was known to have been extensively experimented on by the totalitarian government (Alliance), including having her amygdala removed.
- The characters of Bennett Halverson and River Tam also share notable similarities. Both are so-called "off-the-chart smart" geniuses, and both have a tendency to talk to herself and/or speak in incoherent sentences every now and then.
- Bennett's social security number, revealed in Getting Closer is 549-24-1889. Based on the first 3 digits, this tells us that, although she works in the D.C. Dollhouse, she was actually born in California.