"GLaDOS (Genetic Lifeform and Disk Operating System) is a fictional artificially intelligent computer system found in the Valve Software video game Portal, voiced by Ellen McLain. She initially appears as a voice to guide and aid Chell, the player's character, through the game's chambers, but over time, her words and actions become increasingly malicious, and she makes multiple attempts to kill Chell. After a face-to-face confrontation with GLaDOS, Chell destroys her and escapes. GLaDOS was universally praised for her contributions to the quality of Portal's writing, winning multiple awards for best new character from GameSpy, GamePro, and X-Play."
Source: Wikipedia, "GLaDOS", available under the CC-BY-SA License.