The Clues to Chell's Background in Portal 2

In Portal 2, GLaDOS and later Wheatley make fun of Chell because she's supposedly orphaned. While we can't take anything GLaDOS says at face value, there are some clues in the game that may give answers as to who Chell's parents are. There are also some theories that are tempting to believe, but ultimately don't make sense.

Why is GLaDOS constantly telling Chell she's orphaned?
The obvious reason is it's a good way to insult her. But, is there some truth hidden in the taunts? GLaDOS was activated during Aperture's "Bring Your Daughter to Work" day. It's quite possible one or both of Chell's parents might have been Aperture employees. When GLaDOS was awakened, she promptly filled the facility with neurotoxin, killing just about everyone and locking down the building. We know Doug "Ratman" Rattman survived. He's the one who scribbled in his "dens" in both Portal games. What happened to Chell during the neurotoxin attack is not known. She must have been inside the facility and survived.

Where the clues are
The most telling clue is a potato science project in the Escape chapter of Portal 2. While on their way to shut off GLaDOS' neurotoxin control, Wheatley and Chell walk through children's science projects. Most of them are potato batteries. There is one that is severely overgrown. On the bottom of the project, you can clearly see it is signed by "Chell." Also, on the project, Chell notes she used "a special ingredient from Daddy's work." This is pretty solid proof that Chell had a father that was an Aperture scientist. She wasn't a clone or unloved orphan. She had a daddy who brought his daughter to work. It's also a safe bet that she spent the rest of her childhood as a prisoner of GLaDOS and probably stuck in stasis. It's probably true that if Chell was orphaned, it's GLaDOS' fault.

Another clue isn't in the games, but in the Lab Rat comic released by Valve shortly before Portal 2. In the comic, we can see Chell's personal file. Her last name is blocked out, but other information is visible. It also says the she's incredibly stubborn and shouldn't be tested. It's because of her tenacity that Rattman moves her to the front of the testing line in Portal, in hopes that she's the one that can destroy GLaDOS.

Other "clues" that don't quite fit
One of the most intriguing plot twists in Portal 2 is that Cave Johnson's assistant, Caroline, is where GLaDOS' consciousness came from. During the Old Aperture sections of the game, Chell is greeted by Johnson's recordings blasting over the sound system. Caroline sounds like a happy, helpful assistant. As Aperture starts to lose creditability and money, Cave grows more restless and bitter. His dying wish is that Caroline run the facility in his place.

Cave and Caroline must has been close. They certainly sound like they liked and respected each other. These brief glimpses into their relationship gave way to a theory that they are Chell's parents. The biggest reason this doesn't fit is the clear difference in ethic backgrounds. There's painting of Cave and Caroline hidden in first test chamber of the seventh chapter. It looks like they are both Caucasian, while Chell is not. She's modeled after a Brazilian/Japanese actress Alesia Toyoko Glidewell. It's clear in the game that Chell looks nothing like Cave or Caroline.

The only things that gives this theory weight is why Chell's last name was blacked out in her file and that her father was a scientist. It would make sense if that she was related to Cave, her identity would be hidden. It's also just as easy to speculate that her father was another important scientist.

There isn't a definite answer to who her parents are, but there are many hints within the games. While some are obliviously true, like Chell's name on the science project, I believe others like the Cave/ Caroline relationship are unintentional. The Portal series in a gaming phenomenon. It's only natural that fans speculate and try to make pieces of information fit.