Primarily used in religious contexts to refer to someone who holds beliefs contrary to orthodox doctrine.
In the Middle Ages, heretics were sometimes burned at the stake.
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.
He is known as an iconoclast in academic circles.
That politician is treated as a rebel within the party.
反逆者 emphasizes active rebellion or treason against authority, whereas 異端者 focuses on deviating from accepted beliefs or norms.
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.