character, fictional character, fictitious character - an imaginary person represented in a work of fiction (play or film or story); "she is the main character in the novel"

antihero - a protagonist who lacks the characteristics that would make him a hero (or her a heroine)

contestant - a person who participates in competitions

antagonistic muscle - (physiology) a muscle that opposes the action of another; "the biceps and triceps are antagonistic muscles"

drug - a substance that is used as a medicine or narcotic

biochemistry - the organic chemistry of compounds and processes occuring in organisms; the effort to understand biology within the context of chemistry