There are many changes that John Proctor, a protagonist from Arthur Miller's play The Crucible, goes through over the course of the play.
In the beginning, readers, or watchers, of the play come to find out that he had committed adultery (given his affair with Abigail Williams). This tends to set readers against him as a character. When readers see him with his wife, soon after finding out about the affair, the relationship certainly seems strained. His behavior and attitude towards Elizabeth seems hurtful and mean.
When the people of Salem begin to be accused of witchcraft, Elizabeth pleads with John to go to court and tell them about Abigail admitting to him that the problems the town is facing has nothing to do with witchcraft. He, worried about the affair coming out, refuses (initially). Readers still see a man concerned with only himself.
It is not until Elizabeth is named as a potential witch that John realizes that he must come out against Abigail. Here is where John truly changes. Readers come to see a very different side of John. He loves his wife and is willing to do whatever it takes to save her life. In the end, he willing gives up his own life to insure that the hysteria ends.
Therefore, over the course of the play, John goes from being an adulterous man to one the whole town can raise up and one his wife can truly forgive.