Chell

After GLaDOS and Chell have settled that their quarrel will never be put into an end, the former seemingly utilizes this as a reason to discard Chell from the Enrichment Center; where she is brought to the surface and is given the freedom to lead the rest of her life.

Background
Although Chell's origins are unknown, she was definitely among the people present during GLaDOS' activation in 200-, as GLaDOS locked down the facility immediately afterward; information revealed in Portal 2 implies that Chell was the child of an Aperture scientist and was touring the facility on Bring Your Daughter To Work Day when GLaDOS took over. According to the psychological profile in her personnel file, Chell is "abnormally stubborn" and refuses to ever give up, no matter how daunting the challenge. Originally, she was rejected as a test subject, but Doug Rattmann altered the testing order, having correctly guessed that Chell's extreme tenacity might allow her to defeat GLaDOS.