As a silent protagonist, relatively little is actually known about Chell or her personality in the games themselves. However, the Lab Rat comic shows portions of her personnel file. According to the file, psychological testing showed that Chell scored well into the 99th percentile on the trait of tenacity. A note on these test results characterized her as "abnormally stubborn," adding that "she never gives up. Ever." Because she was so much an outlier in this respect, she was initially rejected for testing until Rattman altered the records.
Rattman's comments imply that Chell's profile was not particularly remarkable in other respects. She was not the fastest or most athletic of the test subjects GLaDOS captured, and some of the others had higher IQs, although Rattman implies that Chell's IQ was above the average. Based on her accomplishments in the games, it can be surmised that Chell is highly resourceful, quick-thinking, good at creative problem-solving, and does not panic easily.
Chell never speaks to GLaDOS. In the first game, GLaDOS asks "Are you even listening to me?" and in the second, she calls Chell a "dangerous, mute lunatic."
However, Eric Wolpaw has stated that Chell is probably capable of speaking, but refuses to do so in order to avoid giving GLaDOS the satisfaction of a response.
The Lab Rat comic showed that Chell declined to answer at least part of her test subject questionnaire, suggesting that her defiant refusal to answer GLaDOS may be a long-standing habit.
At the beginning of Portal 2, when Wheatley asks her to speak, she jumps instead, which Wheatley interprets as a sign of brain damage.
Little else is known about Chell; all further information about her comes from comments by GLaDOS, who is by no means a reliable source of information.
GLaDOS claims that Chell is "a bitter, unlikable loner," "pointlessly cruel," and that objective test results show that she is "a horrible person." As GLaDOS lies habitually about many subjects and has a particular interest in trying to make Chell feel uncomfortable, guilty, or worthless, none of her comments can be assumed to be fact.
