Christian in John Bunyan's The Pilgrim's Progress is the protagonist of the tale and also the title character. In other words, he is the pilgrim who progresses "from this world to that which is to come." Thus we can see that he represents each person who passes from this life ("this world") to the next. Christian is what is known in literature as the "everyman"—that is, someone who represents the common or typical person. Such a character is meant to arouse sympathy in readers, because readers can easily imagine themselves as the character. In a didactic allegory such as The Pilgrim's Progress, the character is designed to teach the reader the lesson more powerfully, because the reader will hopefully internalize what the character learns throughout the story.
It would be simplistic and not completely accurate to say that Christian represents every Christian. Although much of the book relates to Christian's journey as a Christian, he is not a Christian when the tale begins. At the beginning of the story, he is weighed down by sin and fear of God's wrath. He is miserable because he doesn't know how to find salvation. Evangelist appears and points him to the Wicket Gate. When he passes through the gate, he becomes a Christian, and his journey continues until he crosses over to the Celestial City, which represents Heaven and the afterlife.
Part of the lesson of the allegory is that every person is tormented by guilt and the knowledge of sin unless and until he puts his faith in Jesus Christ, whom the Wicket Gate symbolizes. Ignoring false guides like Mr. Worldly Wiseman, Legality, and Civility and trusting in Christ alone results in salvation. After Christian's conversion, he represents not every person, but every Christian believer. By beginning the story before Christian becomes a Christian, Bunyan is able to use his everyman character to illustrate both the way of salvation and the path of the Christian following conversion.