A rebel is a person who exists outside of the regular culture, or who goes against a culture’s norms.
Uncle Axel is a rebel because he knows about David’s secret ability, which makes him illegal, and he doesn’t turn him in. In David’s culture, anyone who is unusual is very dangerous. Just by knowing David’s secret, he is putting himself at great risk. When David tells him that he is listening to other people, he is shocked at first, but then he tells David to keep it a secret, to protect him.
I want you to keep it secret. I want you to promise that you will never, never tell anyone else what you have just told me -- never. It's very important: later on you'll understand better how important it is. (Ch. 4)
Uncle Axel is a good friend to David. He is looking out for him. He is less interested in the rigid orthodoxy of his government than he is who David is as a person. He knows that turning in David because he has this gift is wrong, so instead he protects him and gives him guidance to help him protect himself.
Gordon is a rebel because he has been expelled (for having long arms), and he has created a government of his own out on the fringes. David considers him barbaric, especially because of his association with Sophie. David sees a benefit to the life that Gordon lives.
'But you can be your own selves. You don't have to live a pretence. You don't have to watch yourselves every moment, and think twice whenever you open your mouths.' (Ch. 14)
Gordon is a rebel because he was forced to be. He was forced out, because of his long arms. He did not meet the standard. Because of this, he does not get to live a normal life. He lives a life of hiding, and as Sophie points out, desolation. All of the women are infertile, because they have been sterilized.
Anne is one of the telepaths that David communicates with. She is originally the eldest, at thirteen. She is a different kind of rebel because she chooses to marry. She wants to be normal, and ignore her gift. However, things do not end up well for her. The other telepaths try to tell her it won’t work, and she can’t keep up appearances that long.
I'm a woman -- I've a right to marry and have children. There are three of you and five of us. Are you saying that two of us must never marry? Never have any lives or homes of our own? (Ch. 10)
Anne becomes distant. One Sunday, Anne’s husband is found dead. She refuses to talk to them. She seems to think one of the other telepaths did it. Anne kills herself, and David remembers her as “a limp figure hanging from a beam.” The image haunts him.
Although all of these characters are rebels in different ways, the thread that connects them is that they all do not fit the mold of their society, and they all have an influence on David.