GLaDOS (Genetic Lifeform and Disk Operating System) is a fictional artificially intelligent computer system appearing in the video games Portal, Portal 2, and Lego Dimensions. The character was created by Erik Wolpaw and Kim Swift and voiced by Ellen McLain. GLaDOS is responsible for testing and maintenance in the Aperture Science research facility in both titles. 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. The game reveals that she is corrupted and used a neurotoxin to kill the scientists in the laboratory before the events of Portal. She is ostensibly destroyed at the end of the first game but returns in the sequel, in which she is comically supplanted and temporarily stuck on a potato battery.
The inspiration for the character's creation extends from Wolpaw's use of a text-to-speech program while writing lines for the video game Psychonauts. Other game developers working on Psychonauts found the lines funnier as a result of the synthesized voice. GLaDOS was originally intended to be present solely in the first area of Portal; she was well received by other designers and her role was expanded as a result. Play testers were motivated to complete tests in the game due to her guidance. While the game was initially designed with other characters, they were later removed, leaving GLaDOS as the only character players encounter. The physical appearance of GLaDOS went through several designs, one of which featured a large disk below her. McLain imitated dialog read aloud by a speech synthesizer with her own voice, which was then processed to sound more robotic, and performed songs in character during the closing credits of both entries in the series. " Still Alive" became hugely successful, notably appearing in the Rock Band game series, and has been a popular song for YouTube users to cover.
GLaDOS has been well received by critics and gamers, some of whom called her narcissistic, passive-aggressive, sinister, and witty. She is considered one of the greatest video game characters, particularly among those created between 2000 and 2009. Universally praised for her contributions to the caliber of Portals narrative, GLaDOS received multiple awards for being the best new game character in 2007 from GameSpy, GamePro, and X-Play. A number of publications listed her as one of the all-time greatest video game villains, including IGN and Game Informer, both of which ranked her first. She has been the subject of significant critical analysis from both journalists and game developers, who have compared her to other villainous computer systems in fiction, including HAL 9000 from 2001: A Space Odyssey and SHODAN from System Shock.