GLaDOS (Genetic Lifeform and Disk Operating System) is an artificial intelligence created by Aperture Science and the main antagonist of the Portal series. She is responsible for the testing and maintenance of the Aperture Science research facility and its Test Subjects.
In Portal, GLaDOS initially appears as a voice guide, designed to aid the Chell through the test chambers, but it quickly becomes apparent, through her words and actions, that her intentions are malicious in nature. As the story unfolds, it is learned that GLaDOS used a neurotoxin to kill all the scientists in the lab before the events of Portal.
In Portal 2, GLaDOS resumes her role as test monitor after Wheatley inadvertently reactivates her. She makes no attempt to hide her contempt and hatred for Chell. When Wheatley convinces Chell to perform a core transfer, putting him in charge of the facility, he almost power-crazed and turns GLaDOS into a potato battery. He then turns on Chell and sends both Chell and GLaDOS into the bowels of the facility, where the two must team up to defeat Wheatley. The game reveals an incredible amount of GLaDOS' back story as Cave Johnson assistant, Caroline, and reveals many early Aperture Science creations that were not seen in the first game.
