When John Proctor first appears on stage in The Crucible, Miller tells us quite a lot about him. First of all, we're told how old he is and what he does for a living: he's a thirty-year-old farmer. From this information, we're able to visualize what he looks like.
More importantly for what happens later on in the play, we're told that Proctor is a man with no time for hypocrites or fools. Straight away, we can see that this is the kind of man who won't accept the Salem witch-craze, as this will be based on just those negative qualities that Proctor despises, namely hypocrisy and foolishness.
Despite his admirable qualities, however, Proctor is far from perfect. In the character sketch that accompanies his arrival on stage, Proctor is described as a sinner not just against society's moral values, but also against his own high principles, his “vision of decent conduct.” This is undoubtedly an allusion to his affair with Abigail Williams.
What this information also shows us is that Proctor is a complicated and flawed man who is tormented by his inability to live up to his own principles. To a large extent, Proctor will continue to be thus tormented throughout the rest of the play.