GLaDOS

"So, how are you holding up? Because I'm a potato."

- GLaDOS after being turned into a potato by Wheatley. "You know, deleting Caroline just now taught me a valuable lesson. The best solution to a problem is usually the easiest one. And I'll be honest - killing you is hard. You know what my days used to be like? I just tested. Nobody murdered me, or put me in a potato, or fed me to birds. I had a pretty good life. And then you showed up. You dangerous, mute lunatic. So you know what? You win. Just go. Its been fun. Don't come back."

- GLaDOS freeing Chell at the end of Portal 2.

The Genetic Lifeform and Disk Operating System, also known as GLaDOS, is a major character of the first person puzzle Portal franchise as the main antagonist of the first game, and the first half of Portal 2, before she becomes the deuteragonist in the second half following Wheatley's betrayal.

She was voiced by Ellen McLain.

Personality
GLaDOS' personality core defines her as being a clandestine, surreptitious, manipulative, and revenge-obsessed test master. She speaks in an extremely cold monotone, and does not display any emotion, at least towards Chell and remains incredibly calm through most of her appearances, a rare example of when GLaDOS would display emotion was when she was removed from her body and replaced with Wheatley which prompted her to scream out in pain. Another occasion is when she was left verbally frustrated when Wheatley gave an incorrect answer to her paradox. GLaDOS has many passions such as singing opera (which is a nod to the actress who plays her), baking cakes and a love for science.

Her only purpose in "life" was to force people to complete her tests and then get results, it is revealed that this was do to a compulsive need as when she does not test she gets a terrible "itch". GLaDOS promises to free the captive if they complete all of her tests; however, this took an estimate of sixty years, she either didn't realize or didn't care that the captive would be dead when they were completed. GLaDOS was an emotional sadist and a torturous psychological abuser, after imprisoning Chell in her tests she continues to mock her with cold, disturbing facts and dry cutting insults. GLaDOS continuously insults Chell over being on a orphan and friendless, and insinuates that she is fat. GLaDOS gives facts she describes as interesting but uses to jab her captive such as saying that Chell is breathing the same air the rest of her life or even just flatly saying "I hate you.".

Although (at first), GLaDOS was only passionate and temperamental about completing her tests as Chell began to defy her GLaDOS's insane, deceiving, and narcissistic nature slowly began to develop, focusing all of her near-omnipotent control over the Aperture Science Enrichment Center to kill or torment Chell. GLaDOS had a tendency to frequently lie about her current emotional state, and she would never admit when she was frustrated or angry.

However, when she was turned into a potato by the power-crazed Wheatley, her personality began to diverse. She developed ornithophobia, a crippling fear of birds after nearly being eaten by one, and became a more compassionate, optimistic, and kinder person after discovering that her mind was created using Cave Johnson's (who was the CEO of Aperture science) assistant, Caroline. GLaDOS (or POTaTOS) was able to bury the hatchet, if not for a personal goal, and helped Chell defeat Wheatley, so she could return her to her body and control Aperture Science once again, and in return, GLaDOS would free Chell.

When Wheatley was defeated and GLaDOS was returned to her original body, she returned to her malevolent, cynical, and evil self when she deleted Caroline's program from her mind. However, she did not kill Chell and fulfilled her deal by releasing her from the Aperature Science Enrichment Center (although she claims that this is because Chell is simply too hard to kill) and coldly warns her to never come back.

Past
GLaDOS' origins are gradually revealed in the later stages of the games. An abandoned slideshow presentation in a meeting room shows GLaDOS was developed by Aperture Science Laboratories Inc. as a method of de-icing fuel lines in direct competition with a similar project by Black Mesa Research. GLaDOS is described as not only being a fuel line de-icer, but being fully-functional and "arguably alive". However, GLaDOS is much more than what she was originally intended for; the AI is installed as the Enrichment Center's central control computer. GLaDOS' core is mounted in a large, sealed chamber alongside control consoles and an incinerator. The core hangs from the ceiling surrounded by video screens that show random and irrelevant images. The core swings continuously, dislodging one of the modules in the final level. There are no clear speakers or units which create GLaDOS' voice, though it is present throughout the facility. During the final battle, GLaDOS reveals it is the source of the facility's abandoned state; she flooded the Enrichment Center with a deadly neurotoxin, presumably killing several scientists, just before her Morality Core was installed. Since the core had been installed, it can be assumed that the release happened as the core was being installed, forcing the scientists (at least, those who survived) to abandon the facility.

Portal
GLaDOS works to see how experimental technology is handled at the hands of test subjects. As the game progresses, she increasingly becomes more and more violent; trying to kill Chell many times by means of a fire pit and putting her in a "live fire course, designed for military androids" because the current testing room was undergoing "maintenance." She also psychologically abuses Chell in many cases. One example of this is found in the infamous "companion cube" incident, where she says the Companion Cube must be "euthanized", which is a very helpful object that Chell takes with her throughout the 17th level, characterized by the pink heart design on its sides. Many players get very, very attached to this cube. When a player finally incinerates it (they can't move on in the game if they don't), GLaDOS congratulates Chell on the fact that she incinerated her companion cube "faster than any other test subject on record."

Once Chell leaves the approved course, she eventually finds the main chamber where GLaDOS' chassis is. After a short conversation, a piece of her falls out (the Morality Core). GLaDOS falsely claims she "has no clue what it is". When this piece is dropped into the incinerator, GLaDOS' voice becomes darker and more ominous and she tells Chell "Good news. I figured out what that thing you just incinerated did. It was a morality core they installed after I flooded the enrichment center with a deadly neurotoxin to make me stop flooding the enrichment center with a deadly neurotoxin." (this is also a lie; she knew about the core the whole time). Immediately, she starts to flood the room with said neurotoxin and the boss battle begins. During the battle, the large screens in the room display a clock counting down six minutes until the room completely fills with neurotoxin. Also, a rocket turret, which GLaDOS apparently cannot shut off because the Morality core apparently had some "ancillary responsibilities," appear on the floor and shoots laser-guided rockets at Chell.

To defeat GLaDOS, Chell (the player) must use her Portal Device to redirect the rockets at GLaDOS (making her remaining three cores fall off one at a time) within the time limit. Chell can then drop the cores into the nearby (and very convenient) Emergency Intelligence Incinerator. The three cores which Chell has to destroy (not counting the fourth "morality" core) are Curiosity, Info/Logic, and Anger. As Chell incinerates these cores, GLaDOS's insults gradually become more childish and harsh. She also loses some of her logic, stating that "two plus two is... ten" and correcting herself with "in base four, I'M FINE!"

Once Chell beats her, GLaDOS is sucked through the roof via a portal as she breaks apart. Chell, after being sucked up with her, lands in the parking lot of the Aperture Science Facility, where burning pieces of GLaDOS fall from the sky. However, Chell is dragged away by a party associate robot back into the facility.

Portal 2
GLaDOS returns as the deuteragonist/anti-heroine in Portal 2, which takes place an indefinite amount of time after Portal. At the start of the game, she is still "dead" after being destroyed at the end of the first game, but later is accidentally reactivated by Wheatley, the personality sphere. The newly-reactivated GLaDOS seemingly crushes Wheatley (possibly to avoid a core transfer), and proceeds to take revenge on Chell by dropping her further into the facility and making her endure further tests, all the while making contemptuous and snide comments about her weight and status as an orphan. Eventually, Wheatley appears again and with his help, Chell escapes into the facility, shuts down the turret reproduction line, demolishes the neurotoxin generator, and reaches GLaDOS' chamber again, where she proceeds to use an override system to replace the sadistic AI with Wheatley as the head of the facility.

Just then, in a moment to spite Wheatley, GLaDOS reveals what Wheatley's true nature was: an AI deliberately built to make poor and ignorant decisions in an attempt by former Aperture employees to negate GLaDOS' intimidating and murderous nature. In a rage, Wheatley installed GLaDOS into a potato battery, and when GLaDOS furiously exclaimed that Wheatley was "the moron they built to make [her] an idiot," Wheatley smashed the elevator that Chell and GLaDOS were on, dropping them several miles into the now outdated and sealed off sections of Aperture Laboratories.

During one portion of the game following this, Chell is guided by the voice of Cave Johnson, the founder of Aperture Science and, through these recordings, it is revealed that Johnson intended to copy his personality into a computer to gain immortality and continue watching over the experiments after his death, but died before this technology could be completed, due to exposure to poisonous moon rocks used to make the surfaces compatible with portals, and handed the responsibility of becoming the facility's computer to his personal assistant, Caroline, whose mind was used in creating GLaDOS. During her time as a potato, GLaDOS develops a fear of birds when a crow starts eating her. Only Chell's appearance scares it off.

Eventually, Chell reaches Wheatley and, with the assistance of GLaDOS, who has now become her friend after discovering her true self (echoing the confrontation earlier in the game), attaches corrupted cores to Wheatley. When Wheatley's core corruption has reached 100%, Chell attempts to transfer GLaDOS back into her body, but Wheatley disrupts the core transfer by rigging the stalemate resolution button to explode. As the facility crumbles, Chell shoots a portal underneath Wheatley and to the moon, with the escaping oxygen sucking Chell, the Space Sphere, and Wheatley out. Chell clings on to Wheatley, until GLaDOS detaches him from her mainframe, and pulls her back into the portal and in the facility. However, after being reinstalled, GLaDOS abruptly deletes her program of Caroline's loving personality, becoming a cold, evil machine once again. However, she did not delete Caroline herself because that is her genetic life-form component. If she actually deleted it, the facility would explode. Luckily, she still lets Chell go because she has decided that Chell's presence has been the cause of all her troubles since the first Portal game. GLaDOS releases her into the deserted outside world and, as a final act of indifference, tosses up a charred Companion Cube as well.

Once Chell is gone, GLaDOS sends two robots (Atlas and P-Body) to continue doing tests for her. However, it soon becomes apparent to GLaDOS that testing with the robots is not the same as testing with humans, for the potential threat of death that hung over human heads does not concern the robots; thus, she is unable to get a sick and twisted kick out of the death of the test subjects.

During these tests, GLaDOS sends the robots outside of the testing tracks to find information that will give her complete control over the whole facility. Once she gains control of everything, she sends the bots down into the bowels of the facility. She then reveals why she had the robots go outside the test courses: she's been after a massive amount of humans hidden in a cryogenic vault since the 20th century this entire time. Once the robots unlock the vault, GLaDOS destroys them and begins processing all of the humans, but she only bothers to use the file of one person.

She planned to take her testing even further by turning the humans into her army of minions (what she intended to do with them once training was done was never explained, but it could be possible that intended to use them to take over the world). Unfortunately, the humans were unable to withstand her overly-stressful testing and all of them died within a week's time. With the facility falling to pieces thanks due to a prototype version of her chassis being controlled by an unknown source and the total lack of test subjects, GLaDOS brought the robots back into the fray.

Treating the tests as an art museum at first, GLaDOS tried to fool the robots into thinking that science was finished. However, when a flood began to occur within the facility and it was made clear that the test chambers were thrown together haphazardly, GLaDOS admitted to the truth. She then began to train the robots even more excessively than before so that they could become murderous automatons.

However, once the robots reached the room housing the prototype chassis, it was revealed that the "unknown source" was actually the bird from the bowels of the facility, which had made a nest on the keyboard of the device. Though terrified of the bird and claiming that the robots were not ready for this, they managed to scare off the bird. The only thing that was left over was a nest full of eggs.

GLaDOS relocates the birds into the central AI chamber and, though she treats them as poorly as she treated Chell, when she sees the birds break the glass container that they were in, she has a change of heart and decides that the birds may be of use to her.

Lego Dimensions
In LEGO Dimensions, GLaDOS makes an appearance as a boss in the main story of the game, being fought by Batman, Wildstyle, and Gandalf, as well as in a special stage where she is fought by Chell and Wheatley.

Trivia

 * Caroline, the woman whose mind became the basis of GLaDOS and personal assistant of Aperture Science, is theorized by many to possibly the mother of Chell (the father likely being Cave Johnson himself):
 * At the end of the game, during the "Turret Opera", the lyrics translated into English basically say, in short: "Farewell, my daughter; stay away from science."
 * 40 potato batteries and a baking soda volcano project made by children can be found in the depths of Aperture as remnants of a "Bring Your Daughter to Work Day". One of these projects features a potato that has since then grown through the roof; Chell's name is on it, indicating that she had a connection to the facility as a child.
 * The fact Caroline's mind being the basis of GLaDOS constantly makes people think that her entire self became what GLaDOS is, but that is wrong: the GLaDOS artificial intelligence only has Caroline's mind's way of responding to situations (it can be seen as an example when she first listen to Cave Johnson's voice in Portal 2, both she and the recorded voice of Caroline say "Good morning, Mr. Johnson").
 * GLaDOS is never referred to by name in either the first or second Portal game. Only "she" and "her", particularly by Wheatley.
 * In LEGO Dimensions, GLaDOS speaks Wheatley's name for the first time.
 * WatchMojo.com listed GLaDOS as #2 on their Top 10 Video Game Villains list.