The inspiration for her creation extends from Wolpaw's use of a text-to-speech program while writing lines for the video game Psychonauts. OtherPsychonauts 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 GLaDOS as the only character players encounter. The physical appearance of GLaDOS went 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 processed to sound more robotic. She also sang the lyrics for "Still Alive", written by Jonathan Coulton, which played during the credits of Portal. The song became hugely successful; it appeared in the Rock Band 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 to 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. A number of websites and magazines listed her as one of the greatest video game villains, including IGN, which ranked her first all-time. She has been the subject of significant analysis from both journalists and video 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.Edit
For much of Portal, GLaDOS is a voice that acts as a narrator and guide for players. Her voice is robotic, but distinctly female. Over time, players learn that she is in fact leading the player-character Chell to her death. Her personality has been described as passive-aggressive, witty, narcissistic, and sinister. She has a number of system personality cores installed into her, partly in order to prevent her from killing anyone (other than the ones she already did before the failsafes were installed). Eventually, once the player encounters her, she is revealed to be a complex computer, with robotic parts hanging from a larger device. Once the player removes the first personality core, the morality core, GLaDOS' voice becomes less robotic and more sensual. Originally, GLaDOS was designed as an artificial intelligence and research assistant meant to aid Aperture Science in their goal of beating Black Mesa to the creation of portal technology. Later proposed uses for GLaDOS included implementation as a fuel line ice inhibitor and disk operating system. The AI of GLaDOS is installed as the Enrichment Center's central control computer, mounted in a large, sealed chamber alongside control consoles and an incinerator, which is eventually used to destroy her.
In Portal 2, a character named Wheatley is introduced. It is eventually revealed that he was a personality core that was once attached to her, and was designed to give her bad ideas to inhibit her personality. It is also learned that while she is attached to the Aperture Science facility, she is driven to test, and given a euphoric sensation when a test is complete. However, once she is removed from her position, she begins to act more civil with Chell. It further emerges that GLaDOS has inherited the personality of a woman named Caroline who worked as a personal assistant to Aperture Science's CEO Cave Johnson. She is much warmer when under the influence of Caroline's personality.
In Portal, she is Chell's only link with the situation she is placed in; at the game's start, GLaDOS introduces Chell to the game's Enrichment Center and the physics of the portal gun. In later stages of the center, GLaDOS admits to having lied to Chell about her progress, as part of a supposed 'test protocol.' GLaDOS slowly becomes more sinister, and Chell's trust in GLaDOS is tested when the AI directs Chell into a testing area populated with live-fire turrets, a course designed for military androids. The AI claims that the regular test chamber is unavailable due to "mandatory scheduled maintenance". GLaDOS uses the lure of cake and grief counseling to encourage Chell to continue, but at the final testing area, as Chell prepares to receive the supposed cake, GLaDOS attempts to incinerate Chell in a fire pit. Once Chell escapes, GLaDOS attempts to reconcile with Chell, claiming the pit was a final test.
Chell then travels through the bowels of the Enrichment Center, battling natural hazards and further turrets until she reaches GLaDOS's chamber, where the final encounter occurs. In this encounter Chell dislodges "personality cores" (each also voiced by McLain, with the exception of the final core, which is voiced in a guttural fashion by Mike Patton) and incinerates them. During the battle, it is revealed that before the events of Portal, GLaDOS released a neurotoxin into the Enrichment Center, which resulted in the scientists installing a morality core to stop GLaDOS flooding the Enrichment Center. After the cores are incinerated, the room is sucked into a vortex leading to the surface and GLaDOS is destroyed. Originally the game ended with a fade to black leaving Chell on the surface. This ending was however replaced in a later patch to the game to a new one in which an unconscious Chell is dragged away by the party escort robot (a character referenced earlier in the game). The final scene shows a room filled with more personality cores that begin to light up and a robotic hand puts out a candle on a cake.