GLaDOS

GLaDOS (Genetic Lifeform and Disk Operating System) is the main antagonist of the 2007 video game Portal and the deuteragonist of its 2011 sequel Portal 2. She's an artificial intelligence that oversees the test facility of Aperture Science, created after the uploaded conscience of Cave Johnson's partner, Caroline. While GLaDOS initially appears in the first game to simply be a voice that guides the player, her words and actions become increasingly malicious as she makes her intentions clear. She is apparently destroyed at the end of the first game but returns in the sequel, in which she is supplanted by her former intelligence dampener and temporarily stuck on a potato battery, while her past as the human Caroline is aexplored.

For more information regarding the character, you can take a look at her needlessly long Wikipedia article.