She awoke in a cold cell, walls made of glass with a white, rectangular spot and blue lights on the sides. Disoriented, she stands up, not knowing where she is or how she got there. A loud male voice erupted through a loudspeaker she can't see.
"Hello and welcome to Aperture Laboratories. Before your tests begin, we would like to thank you for volunteering and testing our new scientific inventions. When you reach the end of the test chambers, we'll give you the money we promised." This voice had come from a widely recognizable man. He was Cave Johnson, the CEO of Aperture Laboratories. Everyone knew him from all the ads that he had starred in on the radio.
He promised anyone who volunteered to be a test subject a monetary prize for completing the course. After hearing the announcement, a door opened. She hadn't noticed the door before, but shrugged it off and walked through, collecting a portal gun that she was to use to complete the tests.
Quickly, she raced through the first few tests. She knew she was being watched when she first noticed the scientists observing her actions through a glass window near the ceiling. Not only were the scientists watching, but Cave Johnson as well. Completing each test resulted in praise from him.
Of the thousand people who volunteered, she was the only one to survive. The others had fallen through seemingly bottomless pits or died from the various other obstacles placed in their way. Cave Johnson knew there was something special about this girl. Although shy and quiet, she was a strong woman, and had to be very clever to navigate through the tests and survive.
When she walked through the exit door, Johnson inquired, "How would you like to work here as my personal assistant, Caroline?" The woman had almost forgotten her name. Caroline. It was almost foreign to her. As she opened her mouth for the first time since she started testing, she replied, "Yes. I would love to."
For years, she worked alongside him. Both of them making ads and getting people to volunteers as test subjects for various things like a gel made to speed you up, a gel that acts as a trampoline, combustible lemons, and even injecting mantis DNA into their system. However, the elements that were helping move the science forward was slowly deteriorating the health of Cave Johnson.
Cave Johnson had an idea, and he pitched it to the scientists working for him. "Boys, if we can put music on a CD, is there any reason why we can't put a man's intelligence and personality on one? I want you to figure it out…why haven't I thought of this earlier? If I happen to die before you can put me on a computer, I want Caroline to run the show. I promise you, she will argue and say she can't possibly take my place; Caroline's modest like that. No matter what, you're going to do everything you can to put her in that computer."
A few weeks later, all the employees were at Cave's deathbed, watching the last moments of his life intensely. His last words reiterated the request that Caroline be put into an AI that would continue the tests he started. All the engineers got right to it once Cave Johnson had died. They all knew this was what he wanted. He was right too; the engineers were met with Caroline's modesty. They had to sedate and restrain her while parts of her brain were put into the AI that was made to run the facilities.
Once Caroline's brain was successfully in the machine and her body was put in a preservation tank, they hooked the machine up to the mainframe and gave it a name. It was called the Genetic Lifeform and Disk Operating System, or GLaDOS for short. However, there was a fault in the system. The machine that was once Caroline was now GLaDOS, which brought a complete change in personality. GLaDOS was controlling, manipulative and had an obsession for testing.
Within weeks, GLaDOS had taken over the facility and had most of the scientists become her test subjects. Her testing facilities were built on top of the old ones, the new buildings reaching up above ground level. Cave Johnson's tests were soon forgotten, but there were still many chances of death in the new tests. Toxic waste pits and turrets were what subjects faced when they tested. However, unlike the old tests, hers did not end in a monetary prize; they ended with an element of surprise: immediate death. Throughout the tests, she promised the subjects a cake and a party, things they would never get. The few scientists who still had their jobs desperately tried to fix her itch for testing. It was getting to be too vigorous and too dangerous.
Then came Chell, a woman who was almost as clever as GLaDOS. She was a favourite; GLaDOS' testing itch could be fulfilled. Chell was very smart, and almost as clever as Caroline was, even surviving past the deathtrap at the end of one of the first sections. This rebellion brought about the idea for GLaDOS to make even harder tests, the final one including GLaDOS herself, in fear of Chell being too clever for her.
Chell eventually tore GLaDOS apart, throwing pieces of her into an incinerator. She finally escaped and GLaDOS was in an emergency shutdown state for a while. But upon escape, she was dragged back by robots that GLaDOS had made for security around the facilities. Upon her re-testing and meeting GLaDOS once again, she learns that the last minute of GLaDOS' life was replayed over and over as she relived her death just for the engineer's observations. When she rebooted, her revenge began, and her itch for testing never went away.