Noun
One who engages in any contest; esp. one who in ancient times contended in single combat in behalf of another's honor or rights; or one who acts or speaks in behalf of a person or a cause; a defender; an advocate; a hero.
One who by defeating all rivals, has obtained an acknowledged supremacy in any branch of athetics or game of skill, and is ready to contend with any rival; as, the champion of England.
Source: Webster's dictionary