1) A Crusader is someone who joined the Pope sanctioned wars in the 11th, 12th, and 13th century. They usually joined the Crusades to cleanse their sins or show devotion to God.
2) A staunch attacker of a certain belief, act, etc.
1) The Knight of France was on the Crusade to show that he was a pious supporter of God.
2) Jordan is a Crusader against pedophilia.