The coward inTo Kill a Mockingbirdis Bob Ewell. Bob blames everyone else for his own faults and flaws. He beats Mayella and blames Tom for it. In Chapter 27, after the trial is over, Bob Ewell starts harassing Helen, Tom's widow, as she walks to and from work at Mr. Deas' place. Bob and some of his children had been throwing rocks at Helen. This stops after Deas confronts Bob.
I know every last one of you’s in there a-layin‘ on the floor! Now hear me, Bob Ewell: if I hear one more peep outa my girl Helen about not bein’ able to walk this road I’ll have you in jail before sundown!
Later, Bob starts following Helen. Deas confronts him again and Ewell stops. Not only does he prey on an innocent widow; Bob also uses his children to help carry out his insecurities.
Atticus is the model of courage and honesty in the novel. Take your pick of any quotes by him or about him. In Chapter 23, Atticus shows his courage by taking Bob Ewell's abuse. He explains this restraint to Jem. In this case, choosing not to fight is the courageous option.
Jem, see if you can stand in Bob Ewell’s shoes a minute. I destroyed his last shred of credibility at that trial, if he
had any to begin with. The man had to have some kind of comeback, his kind always does. So if spitting in my face and threatening me saved Mayella Ewell one extra beating, that’s something I’ll gladly take.