Which character in To Kill a Mockingbird is associated with social injustice?

Tom Robinson suffers the most injustice. 

Social justice is the idea that everyone deserves to be treated with respect and have access to equal opportunities.  Tom Robinson faces a great deal of injustice.  He is arrested for raping a white woman, tried, and convicted.  Then he is shot.  All of this is a miscarriage of justice. 

In Maycomb, blacks and whites are not treated equally.  If you are white, you live a life of privilege. Although there are variations due to social class, white citizens will always be better off than black citizens. People in Maycomb just accept that this is the way things have always been. 

Atticus Finch takes Tom Robinson’s case because he is chosen.  He feels that he has an obligation to defend the man to the best of his ability, regardless of how unpopular it might be in Maycomb.  He also tries his best to support his client, even standing up to a lynch mob. 

“You know what we want,” another man said. “Get aside from the door, Mr. Finch.”

“You can turn around and go home again, Walter,” Atticus said pleasantly. “Heck Tate’s around somewhere.”

… “Heck’s bunch’s so deep in the woods they won’t get out till mornin‘.” (Ch. 15) 

In addition to being accused of rape because he is a black man, the mob of white men trying to kill him is another example of social injustice.  The implication is that Tom Robinson, as a black man, does not deserve a trial. Atticus stands up for him and Scout convinces the men to go home. 

The trial itself is only just in that Atticus is defending Tom Robinson.  Atticus is a very well-respected attorney, so Judge Taylor tried to give Robinson a chance.  Atticus does his best to prove that Tom Robinson could not have injured Mayella Ewell because his left arm is crippled and her injuries were on the right side of her face.  Mr. Gilmer treats Robinson very disrespectfully, calling him “boy” and acting dismissively and patronizingly, so much so that Dill had to leave the courtroom crying. 

In the worst social injustice, Tom Robinson is convicted, not because the jury thinks he is guilty, but because he is a black man.  Sadly, he decides that he doesn’t want to take his chances with an appeal and tries to escape.  He is shot going over the prison fence.  Even Mr. Underwood, the newspaperman and an unrepentant racist, believes that this is unjust. 

Mr. Underwood didn’t talk about miscarriages of justice, he was writing so children could understand. Mr. Underwood simply figured it was a sin to kill cripples, be they standing, sitting, or escaping. He likened Tom’s death to the senseless slaughter of songbirds by hunters and children … (Ch. 25) 

Underwood’s point is that convicting Tom Robinson was one thing, but shooting a man with only one good arm is another. Tom Robinson did not deserve to die. There was no reason to shoot him because they could have easily stopped him. Again, he was treated differently because he was a black man.