GLaDOS in Portal 2
GLaDOS, short for Genetic Lifeform and Disk Operating System, is a fictional artificially intelligent computer system in Valve Software's Half-Life video game series in the 2007 video game Portal. She was created by Erik Wolpaw and Kim Swift and is voiced by Ellen McLain. She is responsible for testing and maintenance in Aperture Science research facility in Portal. While she initially appears to simply be a voice to guide and aid the player, her words and actions become increasingly malicious until she makes her intentions clear. At this point the game reveals that she is insane and used a neurotoxin to kill the scientists in the lab before the events of Portal. She is killed at the end by the player-character Chell but is revealed to have survived in the credits song "Still Alive". She appeared in the sequel, Portal 2, which takes place many years after the events of Portal and follows the exploits of GLaDOS, Chell, and other characters.
The inspiration for her creation extends from Wolpaw's use of a text-to-speech program while writing lines for the video game Psychonauts. Other Psychonauts designers were finding the lines funnier as a result of the text-to-speech voice. GLaDOS was originally intended to be used 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 originally designed to have other characters, they later decided to remove them and leave only GLaDOS as the only character players encounter. The physical appearance of GLaDOS had gone through several designs, one which featured a large disk below her.

McLain imitated dialog written in a text-to-speech program with her own voice, which was later converted to sound more robotic. She also sang the lyrics for "Still Alive", written by Jonathan Coulton, which played during the credits of Portal. It must be noted that the song has been a huge success; it appeared in the Rock Band series and has been a popular song for YouTube users to make covers of.

GLaDOS has been well-received by critics and gamers. She has been considered one of the greatest video game characters ever created, particularly for 2000-2009. She was universally praised for her contributions to the quality of Portal's narrative and was awarded multiple awards for best new character in 2007 from GameSpy, GamePro, and X-Play. She has been described as a narcissist, passive-aggressive, sinister, and witty. A number of websites and magazines listed her as one of the greatest video game villains including IGN, which ranked her the all-time greatest. She has been the subject of significant analysis from both journalists and video game developers and has been compared to notable insane computers in fiction, including HAL 9000 from 2001: A Space Odyssey and SHODAN from the System Shock.