GLaDOS is depicted in the series as an artificially superintelligent computer system responsible for testing and maintenance in the Aperture Science Computer-Aided Enrichment Center in all titles.

She is apparently destroyed at the end of the first game but returns in the sequel, in which she is supplanted by her former intelligence dampener and temporarily stuck on a potato battery, while her past as the human Caroline is also explored.

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.

The heroes are forced through more Aperture tests (in which she accuses them of cheating through the usage of the keystones and their abilities) and eventually defeat GLaDOS by introducing her to HAL 9000 to distract her long enough to damage her.

GLaDOS continues to appear in other areas through the main story, adding Portal-themed elements to other worlds and eventually aiding the heroes in defeating the primary antagonist, and on conclusion of the game, she sings a song during the credits, "You Wouldn't Know", again sung by McLain and written by Coulton.

[26] A week later, to alleviate this problem, Wolpaw returned with sample dialogue made with a text-to-speech program, which was intended to be used as a series of messages relayed to the player in the relaxation vault, the first area of the game.

Early designs used for her included a floating brain, a spider-like appearance, and an upside-down version of Sandro Botticelli's painting The Birth of Venus with the four personality cores around her body.

[44] This later led the writers to develop a full story arc for GLaDOS where she would come to recall her past, learn from it to solve the dilemma and then subsequently delete it and reset herself.

[44] This later led the writers to develop a full story arc for GLaDOS where she would come to recall her past, learn from it to solve the dilemma, and then subsequently delete it and reset herself.

Valve provided the developers access to their art assets to include Portal 2-themed content into them, and in some cases, McLain recorded new dialog specifically for these games.

The song has been performed in multiple venues by Jonathan Coulton which includes the Penny Arcade Expo in 2008, the Press Start -Symphony of Games- concert in 2009, and the Game Developers Conference in 2008.

[74][75][76][77] When announcing McLain's addition to the cast, del Toro stated that he is a "big fan of Valve" and highlighted Portal and Left 4 Dead as "instrumental family experiences" in his home.

[107] PC Zone UK listed her as the second-best conceived character in gaming, commenting that the memes related to the Weighted Companion Cube and "the cake is a lie" could distract people from GLaDOS's "perfectly-metered and lyrical voice".

[115] GameSpy's Nathan Meunier wrote that "without inhuman antagonist GLaDOS spewing a laugh-inducing tirade of thinly veiled threats in her deadpan robotic drone as you progress deeper into the bowels of Aperture Science, Portal would have been a very different game".

She is as vindictive as ever, coating pure unadulterated hatred with a veneer of cool science" and that "for fans of GLaDOS, her return from her unfortunate death in the previous Portal is fabulous, and her literal transformation within the game will shock, wow, and humor even jaded gamers tired of cake quotes".

[124] PC Gamer's Dan Stapleton wrote that "evil robot GLaDOS is in top politely murderous form right from the moment she appears on screen" and that "Portal's show-stealing monotone antagonist is challenged for the spotlight by Wheatley".

[129] The Globe and Mail's Chad Sepieha listed the top five insults from GLaDOS in Portal 2, which included "Science has now validated your birth mother's decision to abandon you on a doorstep.

"[130] Rock Paper Shotgun's John Walker wrote that "Ellen McLain returns as GLaDOS, and is pushed so much further this time, hitting every single line with perfection".

[131] Game Informer's Adam Biessener wrote that while Portal 2 was less quotable than its predecessor, "repeating GLaDOS lines stopped being funny a long time ago".

[137] MSNBC game reviewer Blake Snow compared The Sign Painter from World of Goo to GLaDOS, due to the mischievousness and unseen nature of the character.

[140] However, PC Zone UK commented that the comparisons between GLaDOS and SHODAN run dry; while Portal leaves everything to the players' imagination, System Shock 2 has a strongly defined storyline.

[108] The Daily Telegraph editors Nick Cowen and Tom Hoggins listed her as the ninth-greatest video game villain, stating that she is as diabolical as a female AI can get, mentioning SHODAN as being inferior in this respect.

[141] Writer N'Gai Croal commented that the boss battle with GLaDOS is similar to the "Room 19" encounter with Andrew Ryan from BioShock, citing the same use of tactical language and techniques between the two.

[144] Stephen Totilo notes the "artful way" in which GLaDOS's antagonistic character is slowly revealed and defined throughout Portal despite "little interactivity in how the story is told".

[26] Grant Tavinor, author of The Art of Videogames, wrote that GLaDOS's actions and personality in Portal were "in the best of science fiction traditions" and describes her as "insincere, malfunctioning, and probably insane".

: The Guide to Great Video Game Design, uses GLaDOS as an example of a "tormentor" boss character, stating that she taunts and challenges the players, but does not directly confront or attack them.

In response to a quote by designer Erik Wolpaw that read "we wanted you to have this very intimate connection with this AI that changes and evolves over time, leading up to the point that you betray her and do the most intimate act you can do with someone—murdering them in cold blood", he at first noted that "on the face of it, this description of intimacy seems nonsensical", but also noted that "a changing and evolving relationship with someone in authority over you that eventually leads to betraying them by violating their rules—is one that is an altogether familiar one".

In contrast to this, he wrote that "an extremely smart leader can be about the most oppressive force in an organization has already been provided in abundance for anyone who has played the first Portal" and that "GLaDOS's "leadership" is the very definition of sadistic fascism".

[152] G. Christopher Williams wrote that the addition of an "intelligence dampening sphere" performed by scientists on GLaDOS before the events of Portal could represent the "response from men to what they perceive as the 'misbehavior' or 'irrational thinking' of women".

He also wrote "the effort to 'dampen' intelligence becomes a rather literal manifestation of the labeling of women as 'dumb' or 'irrational' and the need to control such 'poor' behavior"; he also cited how Wheatley was given a masculine voice to "remind her that she is dumb and to curb her tendency towards 'misbehavior'".