In To Kill a Mockingbird, Scout and Jem Finch's father, Atticus Finch, tells his son that he must not shoot mockingbirds.
"I'd rather you shoot at tin cans in the back yard, but I know you'll go after birds. Shoot all the bluejays you want, if you can hit 'em, but remember it's a sin to kill a mockingbird."
Scout, who had overheard her father's instructions, later asked Miss Maudie, a trusted friend and neighbor, what her father meant; Scout had never heard her father refer to do something as a sin and did not understand what he meant. Miss Maudie explained it very simply.
"Your father's right," she said. "Mockingbirds don't do one thing but make music for us to enjoy. They don't eat up people's gardens, don't nest in corncribs, they don't do one thing but sing their hearts out for us. That's why it's a sin to kill a mockingbird."
Of course, the mockingbird is symbolic and represents someone who is innocent (pure and good). Tom Robinson is the most obvious "mockingbird" in the novel; he truly has a kind and generous heart, yet he is punished for his goodness when he is found guilty of the rape of Mayella Ewell. Mayella herself is a mockingbird, since she is not to blame for her upbringing or her station in life; Mayella attempts to bring beauty to her home and love to her life.
Although he is not the most prominent example of a "mockingbird" found in To Kill a Mockingbird, Dolphus Raymond is, symbolically, a mockingbird. Scout,Jem, and Dill learn this when Raymond gives Dill a drink of Coca-Cola to make him feel better during the trial of Tom Robinson. The children, like Maycomb society in general, assume that Raymond is a drunk because of the act he puts on in public. When the children realize that he is not a drunk, he explains.
"...you mean why do I pretend? Well, it's very simple," he said. "Some folks don't--like the way I live. Now I could say the hell with 'em, I don't care if they don't like it. I do say I don't care if they don't like it, right enough--but I don't say the hell with 'em, see?...I try to give 'em a reason, you see. It helps folks if they can latch onto a reason...folks can say Dolphus Raymond's in the clutches of whiskey--that's why he won't change his ways. He can't help himself, that's why he lives the way he does...Secretly, Miss Finch, I'm not much of a drinker, but you see they could never, never understand that I live like I do because that's the way I want to live."
Dolphus is a good man who chooses to live with a black woman. The people of Maycomb, who (in general) are not willing to accept Raymond's interracial relationship, at least overlook it because they believe that it is the result of a drinking problem. Because they have a "reason," they do not persecute Raymond or his family for it. Raymond's goodness and innocence in being willing to belittle himself in order to protect his family make him a "mockingbird."
Dolphus Raymon actually isn't considered a mockingbird. Harper Lee showed the two figurative mockingbirds to be Tom Robinson and Boo Radley. Seeing as Raymon doesn't have a big of a part in the story, but if you have a teacher that told you this, then I can't help you. Robinson and Radley are both main characters and they are stereotyped in such a way that makes them seem less to the people of Maycomb. But to the reader, Lee makes it clear that they are the good guys and the people not seeing them for who they are are the bad guys. Does that make sense?