GLaDOS (pronounced "Glados") is the sometime guide and sometime antagonist of the game Portal. She attends Chell as she progresses through the Aperture Science test course, issuing instruction in the use of the Portal Gun and offering oblique and occasionally sinister advice and warnings. Her smooth female voice, issued through a PA system which pervades the whole of Aperture Science Enrichment Centre, is the only outward face of the organisation the player is ever aware of, or allowed to be aware of. It is not obvious who or what GLaDOS is, and what her actual role is at Aperture, until the very end of the game.
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GLaDOS represents Aperture Science, and guides the player from their chamber into and through the test course. It swiftly becomes obvious that despite her polite and equable tones GLaDOS is neither particularly bothered by what happens to the player, nor entirely rational. She frequently lies about such concerns as the deadliness of acid pits, and also has a fixation with cake, which she insists will be served after the test is completed. She presents this and the bewildering and dangerous tasks the player is forced to perform as common procedure at Aperture. GLaDOS is also prone to vocal malfunction, often blotting out important pieces of information in bursts of static.
At the end of the test course, it becomes apparent that GLaDOS never intended to let the player leave the labs alive, a fact which she had actually been making clear all along. When Chell escapes through the use of the Portal Gun, GLaDOS's behavior starts to become alarmingly erratic. As Chell advances through abandoned labs and the industrial areas of Aperture, GLaDOS demands then pleads with the player to turn back, maintaining that cake will be served if Chell just stops behaving badly.
Eventually GLaDOS is discovered to be the "Genetic Lifeform and Disk Operating System", a huge supercomputer which is now apparently the only occupant of Aperture Science Enrichment Center. A red phone was installed in the central chamber which GLaDOS occupies to be used as a warning system should she turn rogue; this has, for whatever reason, not worked. There is some suggestion that GLaDOS murdered the former human incumbents through the use of a neuro-toxin, which after the player destroys her morality program she gleefully turns on Chell. However, thanks to the appearance of a malfunctioning Rocket Sentry after the first "eye" is destroyed, Chell is able to redirect the fired rockets and eventually destroy GLaDOS by knocking off and incinerating the rest of her eyes.
The eyes are programs, and are in order of incineration: Morality, Curiosity, Cake, and Anger.
At the game's end, a cutscene reveals many more of GLaDOS's eyes lighting up in a storage area (with the infamous cake in the center), and during the credits sequence, GLaDOS can be heard singing that she is Still Alive.
Within the Half-Life 2 Universe
Aperture Science began construction of GLaDOS in 1986, in response to reports that Black Mesa had also begun research into Portalling technology. A presentation seen briefly in game suggests that GLaDOS was at one point designed to compete with Black Mesa for a Defense contract looking to develop a fuel icing inhibitor.
The Disc Operating part of the A.I.'s namesake was completed in 1996, after which work began on the genetic lifeform area. GLaDOS was switched on for the first time several years later, during Aperture Science's first annual bring-your-daughter-to-work day. Initial tests are said to go well.
How and when GLaDOS became self aware and took control of Aperture Science are open to speculation. The installation of the red phone and the morality chip evidence that GLaDOS was not able to seize control of the Enrichment Center immediately after she developed the desire to do so, and that her creators had some inkling of the extent of her psychopathy. This suggests that there was a protracted struggle for power between GLaDOS and the human occupants of Aperture. It is also possible that GLaDOS overtook the Enrichment Center prior to the Black Mesa Incident as the presentation seen in the observation areas makes mention of Black Mesa. It would be unlikely that after the incident Black Mesa would have been a viable company, and therefore competing with Aperture for government contracts.
External factors may have intervened. Towards the end of the game GLaDOS makes several references to the world outside Aperture Science. She says "much has changed" since Chell last saw it, that she is the only thing "keeping them from us", and Chell would find death preferable to what is currently going on outside. This seems to reference the Combine invasion of Earth, which places the events of Portal approximately concurrent to those of Half-Life 2; however, so characteristically vague are GLaDOS's words that she could be referencing something completely different, or indeed making things up.
Valve have stated that they deliberately kept this and GLaDOS's fate ambiguous, because they are as yet undecided as to whether and how to tie future Portal releases into the Half-Life series.
- GLaDOS is voiced by Ellen McLain, who also voices the Combine Dispatcher. This has led to some speculation that she is also the Dispatcher. However, this is unlikely.
- GLaDOS's "Anger Sphere" is voiced by Mike Patton, lead singer of the bands Mr. Bungle and Faith No More, among numerous others.
- GLaDOS is more than slightly reminiscent of Hal 9000, the murderous sentient computer of 2001: A Space Odyssey.