noun: a person who is admired for their courageous deeds and imperial qualities.
John Proctor is a man of many faces. Like a hero, he has his weaknesses. He had an internal conflict with being honest and upfront with Elizabeth about the affair with Abigail because he could be tried for adultery if he confessed. Clearly, honesty wasn't his best policy in this case.
When Danforth asked him to sign a written confession, he refused calling it "signing the Devil's book" because he didn't want to be put in that sudden position of being forced to become another follower of their theocracy per say. Like a true hero I believe he stuck to his individual values of nobility and self-accountability even in life or death situations. It's fair to say that Proctor had a guilty conscience not confessing in the beginning when he had the chance to but he was indecisive between the choice of pleasing Elizabeth or pleasing Abigail. To be able confess to adultery for the greater good is a heroic act, one that could take Abigail down rather then the whole town.
Considering that many people lied when confessing in order to live, this is an act of righteousness. In the end, he proves his heroic characteristics by possessing the courage to give a verbal confession while standing his ground.