Most of Chell's history remains a mystery. During the final events of Portal, GLaDOS mentions numerous times that Chell was abandoned at birth, and continued again throughout Portal 2. She later mentions in Portal 2 that Chell was also adopted, though the credibility of GLaDOS' word is left up to the interpreter. Many of GLaDOS' comments throughout Portal 2 and the latter stages of Portal are in an effort to belittle, annoy, or distract Chell from achieving her goal, whether or not statements of her adoption and orphan status are true or not is up for debate.
Portal
At some time frame in 2010, during the introductory sequence of Portal, Chell is awakened in a Relaxation Vault - previously having been unconsciously deployed into it. Curious, she maneuvers around the vault and witnesses the test chamber she has been prepped into. After a mere ten seconds of her awakening, Chell is greeted by a robotic but seemingly automated female voice who addresses to the protagonist in the regard that she is a test subject. The AI, who was later abbreviated as "GLaDOS", then points out that the goal of these tests that she will perform for the company of Aperture Science are to bring an educational experience to their test subjects currently running the courses.
The intimidating AI, GLaDOS, then finally generates two oval-shaped teleportation fabrics (portals) on a solid flat surface, with an entrance portal in the Relaxation Vault and an exit just in front of the exterior of the vault. Chell maneuvers away from the vault, however, she may have possibly noticed the empty observation rooms - lacking the staff that were supposedly recording her performances. After completing her first test of understanding a cube-and-button based mechanic, she was then put through a series of tests to further understand the usage of portals.
Having completed two tests, Chell was finally ready and put into a test chamber where she is to equip the Portal Gun. And later within her testing course, she is put through more dangerous tests with the presence of goo beneath test chambers, deployment of High Energy Pellets into the test, and more. However, thanks to the Advanced Knee Replacement components applied to the back of her lower leg to her ankles, Chell was safe from any potential injury and pain from falling at high velocity from the results of portals and momentum. She was also finally able to replace her single-powered Portal Gun (fires blue portal, where orange portal is generated by the test chamber) with a dual-powered Portal Gun (fires orange and blue portals). Further through the testing, Chell is promised by GLaDOS that the cake would be served at the conclusion of the tests.
However, it later became apparent that GLaDOS would not keep to her promise. Chell stumbles upon various areas with defunct wall panels, and manages a way to sneak into them. As she enters these backstages of a test chamber, she finds refuge areas commonly known as the Rattmann's dens - previously the resting areas for Aperture technician Doug Rattmann. The scribblings of the walls in these dens appear to be a warning for Chell, telling her that "the cake is a lie" and how "she's watching you". Chell now made a bit more aware of her situation, is forced to continue the testing and play along with GLaDOS' plans. And indeed, the warnings were correct as GLaDOS finally decides to lower Chell into a fire pit upon completing the final test chamber, where the cake was said to appear.
Chell successfully escapes the dramatically slow death trap, and was no longer dependent on GLaDOS as the latter makes constant attempts to convince her that "faking" her attempt to kill Chell was part of the test. Upon her escape from the testing tracks, she travels around the facility in hopes of reaching the surface. However, realizing there was no chances of this, she is forced to confront GLaDOS in the Central AI Chamber as the latter awaits her arrival.
Now prepared to face GLaDOS, Chell is greeted by the passive-aggressive rogue AI. GLaDOS fakes attempting to give Chell her surprise, however, before finishing the countdown, a Morality Core was coincidentally detached from the Central AI's body. Chell destroys it via the Emergency Intelligence Incinerator located behind the Central AI Chamber. However, it was a mistake as it was the one thing GLaDOS needed to be disposed of so she can gain further control over the Enrichment Center, as she ultimately unleashes neurotoxin into her chamber to kill Chell off. This causes a Rocket Turret to emerge from a core hatch beside her, but Chell was resourceful and redirected the rocket projectiles through a portal behind her, firing towards GLaDOS instead. She does this repeatedly to continue detaching more personality cores previously attached to her body. However, the further cores she lacked, the more relentless she became. But after Chell destroys the Anger Core, GLaDOS was sent spiraling, literally, into her demise as the destruction of her generators triggered a gravitational pull - where they both end up on the surface before the protagonist went unconscious.
Chell then slowly regained consciousness, and witnesses herself in the parking lot of the Enrichment Center with a lifeless GLaDOS beside her. As Chell regained a clear vision, the Party Escort Bot thanks her for "assuming the party escort submission position" immediately before dragging her back into the now-ruined facility. Little did she know, the destruction of the Central Core, GLaDOS, automatically caused the facility to reactivate warehouses full of personality cores to manage the Enrichment Center as GLaDOS was killed.
