While it's tempting to quickly define Chris as the disabled kid in a wheelchair, he's more than that. He's one of the most thoughtful, considerate characters in the book, although many of the other characters don't take him seriously, or even ignore him. We're not really sure what his condition is. Dr. Deere defines it as "pyramidal tract involvement" (5.31), and what that seems to mean for Chris is that he's in a wheelchair, doesn't have control over his spastic body, and has trouble speaking. His mind, though, is perfectly intact; he brings innocence and pure excitement to the Westing game.
There aren't really any benefits to the illness Chris has. It's especially frustrating to see him juxtaposed with Sydelle, who poses as a "cripple," but is actually perfectly healthy. While she creates an imaginary illness to draw attention to herself, his very real illness causes people to turn away. Yet Sydelle is one of the few people to draw Chris out of his shell and try to make him laugh, suggesting that his wheelchair-bound body is the perfect alibi for a crime like the murder. In a melodramatic mystery, that might very well be the answer: the guy in a wheelchair really doesn't need to be there – he's been hiding in it. Unfortunately for Chris, that isn't how this mystery works.
So how does Chris define himself? As Christos Theodorakis, birdwatcher. He has a deep, abiding interest that he's passionate about, and he works hard to achieve his goal: a birdwatcher is who he becomes, studying ornithology at the university and even discovering rare species of birds. True, he's helped along the way by his brother, who cares for him; Dr. Deere, who encourages him to try new medical treatment; and Judge Ford, who sponsors his education. What they all mostly do, though, is help him escape the boundaries of his body and his financial class, and enable him to become a scholar. You could argue that freedom's a basic human right, but Chris is someone who would see it as a privilege.