noun (n)

• a disputant who advocates reform(noun.person)

  Synonym:
  meliorist, reformer, reformist, social reformer
  

  source: wordnet30
• a warrior who engages in a holy war(noun.person)

  Example:
  The Crusaders tried to recapture the Holy Land from the Muslims.
  

  source: wordnet30
• One engaged in a crusade; as, the crusaders of the Middle Ages.(noun)

  source: webster1913