Caroline

Dossier: CEO Caroline "Backbone" McLain, the assistant
 * Background: Former personal assistant of Cave Johnson, and CEO of Aperture Labs after his departure, although for a short time.
 * Skills: Exceptional in teamwork and takes orders without question.  
 * Reason for hire: "Yes, I have brain damage, sir!" (Subjected to brain mapping for the Aperture Labs GLaDOS AI causing progressive lethal brain damage)
 * Appearance: Long hair, brunette, pink and red handkerchief on her neck. S.C.I. issued a white H.E.V. Mk IV.

Events
After Cave's departure from Aperture, he appointed her as the new CEO in charge, and secretly ordered his employers to force her to be used in the brain-mapping for project GLaDOS.

Cave Johnson was invited to the miracle experiment by Sven Co-op, and according to the contract he had to feign his death for the time being. He still had a few weeks of time though. Not long before Cave was expected to actually die, and shortly after Caroline became the new CEO, she was taken against her will by the executive board and they performed a brain-mapping, effectively copying her consciousness into a machine that would be soon perfected and activated in the coming years.

But the version of the machine at that moment had a recent upgrade. Aperture scientist's had bought some redmetal reverse engineered microchips from the small Daedalus Labs by Turrican, and because it was an unknown and dangerous element for the human body, she was then diagnosed with an unknown kind of brain disease on top of the one the brain-mapping already did by default, thus she was expected to die only in just a few days.

While she was still healthy enough, Sven Co-op contacted her, giving her a chance to be cured. Only after that, days later, she joined the other recruits in the promised experiment where she could be cured.

Her surprise was that Cave was also present as one of the recruits. She would have to struggle between love and hate, but eventually experiencing a new future with him as his backbone once again, with her new split personality disorder acquired as a secondary effect of having the strange redmetal brainwaves leak into her brain...

...which probably also is the reason she sometimes becomes temporarily possessed by a lust for blood and death.