Before development of GLaDOS had begun, Erik Wolpaw was writing the script for the video game Psychonauts, where they went around the office, finding people to provide voices to the words until they could add the final voices to the game. Once they ran out of people, however, he began using a text-to-speech program. According to Wolpaw, people found the lines funnier than they were worth. He commented that "no amount of writing is funnier than this text-to-speech thing reading it".He became bitter about that, stating that he would leverage this and use it to his advantage. The creation of GLaDOS began with a discussion between the Valve team and Wolpaw on the narrative restraints they had to deal with. When they were designing the game, they found that they did not have enough time or staffing to use human characters, due to the amount of animation work and scene choreography involved.
|GLaDOS went through several redesigns before artists settled on the final anthropomorphic shape. Early concepts featured a floating brain and a spider-like appearance|
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. The team liked the voice, describing it as "funny" and "sinister", so Wolpaw decided to add this voice to other test chambers, all the while trying to think of story elements. The developers noticed that play testers were more motivated by the voice because they became attached to it. As a result, the team decided to make GLaDOS the narrative voice of Portal.While designing GLaDOS, one of the rules that the writers had was that they would not make her seem like a computer, using an example line, "Oh my nuts and bolts." While GLaDOS is physically a computer and speaks with a computerized voice, they intended her to speak to the player-character like a regular person.
|The Birth of Venus was the inspiration for one design of GLaDOS, where GLaDOS' physical appearance was similar to the Roman goddess Venus', but upside down.|
GLaDOS' physical appearance went through several iterations when Valve had Jason Brashill help drive the visual creation of GLaDOS. 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. Eventually, they settled on the design of the robotic figure hanging upside down. This was done to convey both a sense of raw mechanical power and femininity.A large disk with the four personality cores hanging from it was added to her design, when she was still just a sphere standing above it. However, the team found it to be too small, giving her a body and putting it below the disk. Another early design was when GLaDOS was only a cube, which was used for the removed laser battle mentioned below.The large chamber that the player-character encounters was the result of the team wanting to build a space that brought a great deal of attention to her.
GLaDOS was written with the intent of making her more understandable and empathetic to players, making her villainy more tragic. Kim Swift, team leader of Portal, described her growth in the game as her becoming more and more human. The two-hour total playtime for Portal allowed the writers enough time to let players get to know GLaDOS.Wolpaw commented that while GLaDOS did yell and fire rockets at the player, she fulfilled his desire for a villain who has not been "done to death". He described her as both supportive and funny, while also sad and scared. One of his intentions was for players to believe that they are "putting her through the wringer emotionally." The game was designed to have a clear beginning, middle, and end. Wolpaw stated that with each new part, GLaDOS' personality changed. She begins as a supportive, yet also increasingly sinister character, where she delivers exposition about the general Aperture mindset. However, once the player-character escapes, she begins to speak in first-person singular rather than first-person plural. She shows desperation due to her lack of control at this point, adding that more emotion begins to creep through her voice. After destroying the morality core, she becomes unhinged, featuring an almost human voice. This voice, described as sultry by Wolpaw, was originally to be used for turrets, but it did not work out. Because they liked it so much, they chose to use it for GLaDOS.Valve described GLaDOS' actions in Portal 2 as attempting to build a relationship with the player-character, and the only way to accomplish this is by testing her.