12. GLaDOS

First appeared in: Portal (2007)

GLaDOS (Genetic Lifeform and Disc Operating System) is the feminine artificial intelligence that acts as your guide through the Aperture Science's Enrichment Centre in Valve's superbly inventive Portal. Spurring the main character on with the promise of cake, GLaDOS initially takes the form of a benevolent overseer - albeit one that makes slightly anomalous and threatening remarks. It's not until she demands the incineration of your much cherished Companion Cube that the player begins to suspect that the screws in this demented AI are quite literally coming loose.

Yet, for all of her malicious HAL-like conduct, as she begins to lose control of your portal-jumping ways, her increasingly demented, robotic taunts - and often, by her own admission, lies - become a constant highlight, with some of the psychotic asides being nothing less than comedy gold. While she appears to have been destroyed at the game's climax, the inspired end-credit song "I'm still alive" bodes well for her triumphant return in Portal 2.