John Proctor is the protagonist of the play The Crucible. He is a farmer who had an affair with a servant girl named Abigail. The servant left his house at his wife's command. Abigail then devises a plot to try to get Proctor away from his wife. She and other girls begin claiming they see people with the devil and they accuse a bunch of people in the town including Proctor's wife. Proctor has to struggle with confessing his guilt to the town or losing his wife. Enotes has a complete character analysis at the link below.
John Proctor is one of the residents of Salem, but unlike almost everyone else, he does not succumb to the madness that consumed Salem, Massachusetts during the time of the Puritans. John lives by convinction, although admittedly (and for a time, begrudingly) makes grave errors in judgment. Still, he refuses to be railroaded into false confession in the end, and chooses death over dishonor.
John is married to Elizabeth, herself accused as a witch, and has an affair with the malicious Abigail, instigator of the whole gruesome affair.