Tom is a humble, hard-working, honest family man whose simple act of charity caused him to be unjustly convicted of raping the poor white woman he was trying to help. Despite his crippled left arm, Tom is an able worker--big and strong, with "broad shoulders and bull-thick neck," and Scout sees that
If he had been whole, he would have been a fine specimen of a man. (Chapter 19)
His testimony is truthful, delivered in stark contrast to the lies told by both Bob and Mayella Ewell. He politely answers each question, addressing Atticus and Gilmer as "sir" (or "suh"). He is hesitant to recall the threat made by Bob to his daughter--"... you goddam whore, I'll kill ya"-- because it's "not fittin' for these folks and chillun to hear." Tom is forced to accept the indignity of the times: He is called "that black nigger yonder" by Bob; he is addressed as "nigger" by Mayella, both in her home and in the courtroom; and he is repeatedly referred to as "boy" by the prosecutor, Horace Gilmer. As Tom freely admits when he is asked by Atticus why he ran if he knew he was innocent,
"Mr. Finch, if you was a nigger like me, you'd run, too." (Chapter 19)
Atticus had known all along that Tom's chances of an acquittal were slim, since there was little chance of convincing an all-white jury of his innocence.
"... the jury couldn't possibly be expected to take Tom Robinson's word against the Ewells'." (Chapter 9)
In the end, Tom decides to flee from the prison walls, having "tired of white men's chances and preferred to take his own."
I dont have the book anymore, but I believe his strengths are that he is a generous, kind, innocent person. As for a quote, you could use one from when the gang goes to TR's jail cell to torture him and Atticus has to stop him. Their racism caused them to be undoubtedly convinced that he comitted the crime and spurred them to go to punish him worse than any other criminal. Sorry I dont have anything to quote from.