3. Shodan

First appeared in: System Shock (1994)

Forget Bowser, Ganondorf and Dr Robotni:, if you're after the most terrifying, psychologically disturbing and downright memorable evil mastermind in video games then look no further than System Shock's Sentient Hyper-Optimized Data Access Network, or SHODAN. The megalomaniacal AI at the heart of Sierra's RPG adventure, SHODAN began life as the benign computer core of Citadel Station, until the game's protagonist (you) hacks her ethical subroutines and makes her self-aware and happily homicidal.

Given that she's never directly seen, SHODAN's constant, threatening presence is a masterstroke of game design: the AI's influence felt through her omniscient control of the station's security cameras, robotic defences and periodic audio transmissions that haunt the player's every move. Speaking in stuttering, discordant fluctuations, her distinctive tones (voiced by former Tribe vocalist Terri Brosius) goad, deride and threaten as you make your way through the bowels of the station. SHODAN's most magnificent performance is reserved for the game's sequel, however, when it's revealed that the benevolent Dr Polito, who has been guiding you through half the game, is actually a stiffening corpse and the 'metal mother' behind the first game has been leading you by the nose all along. Chilling stuff.