Boo Radley and Tom Robinson are described in detail. They are a good choice of pair since they are both the victims of the story, and its symbolic mockingbirds.
Arthur “Boo Radley” is described in two ways. There is the children’s fantastical description of him, and the actual description when Scout sees him at the end. Jem gives a reasonable description of him to Dell. He is described as “about six-and-a-half feet tall, judging from his tracks” with hands that are bloodstained because “if you ate an animal raw, you could never wash the blood off” (ch 1). His description gets more fanciful from there.
There was a long jagged scar that ran across his face; what teeth he had were yellow and rotten; his eyes popped, and he drooled most of the time. (ch 1)
Actually, Boo is a timid, pale, shy man. He never goes outside. His hands are “sickly white hands that had never seen the sun” and he wears “sand-stained khaki pants” and a “torn denim shirt” (ch 29). He is very thin. He has a jutting chin and his face is as white as his hands.
His cheeks were thin to hollowness; his mouth was wide; there were shallow, almost delicate indentations at his temples, and his gray eyes were so colorless I thought he was blind. His hair was dead and thin, almost feathery on top of his head. (ch 29)
When Scout sees Boo for real, she comes to understand him much better.
Tom Robinson is crippled. He is black, and has “powerful shoulders rippled under his thin shirt” (ch 18).
His left arm was fully twelve inches shorter than his right, and hung dead at his side. It ended in a small shriveled hand, and from as far away as the balcony I could see that it was no use to him. (ch 18)
Like Boo, Tom is victimized by society. He also has weaknesses, because he only has use of one arm. The children sympathize with him.
In each case, the physical description of the character contributes to others' attitudes about him. Both men are victimized in large part because of how they look.