John Proctor
Often called the tragic hero of The Crucible, Proctor is likely the most studied character of the play. He struggles with morality and sin throughout all four acts. How does this effect his character? Delve into his moral strengths and weaknesses.

Most of your information will come from a close reading of the actual play. Pay close attention to John's scenes in all four acts.
You might also want to check out the following books:
Bloom,
Harold. Bloom's Reviews: Arthur Miller's The Crucible.
New York: Chelsea House Publishing, 1998.
Johnson,
Claudia Durst, and Vernon E. Johnson. Understanding The Crucible.
New York: Greenwood Publishing, 1998
Martine,
James J. The Crucible: Politics, Property, and Pretense.
New York: Twayne Publishers, 1993.
You can also find information about the real John Proctor at this web site:
http://www.law.umkc.edu/faculty/projects/ftrials/salem/ASAL_BI.HTM