Primarily used in religious contexts to refer to someone who holds beliefs contrary to orthodox doctrine.
nonconformist; freethinker; iconoclast; rebel
Extended to secular contexts: a person who rejects conventional ideas, norms, or authority; often carries a nuance of intellectual independence or defiance.
In the Middle Ages, heretics were sometimes burned at the stake.
He is known as an iconoclast in academic circles.
That politician is treated as a rebel within the party.
Compound of 異端 (itan, 'heresy') + 者 (sha, 'person'). The term 異端 is composed of 異 (i, 'different') and 端 (tan, 'end, edge'), originally referring to a divergent branch or extreme view.