noun
Refers to a person who rebels against established authority, often in a political or military context. Can be used historically or in fiction.
彼は反賊として捕らえられた。
He was captured as a rebel.
その時代、反賊は厳しく処罰された。
In that era, rebels were severely punished.
反逆者 is a more common and general term for a rebel or traitor, while 反賊 has a slightly more historical or literary feel.
Compound of 反 (anti-, against) and 賊 (bandit, rebel). The variant 叛賊 uses 叛 (rebel, defy).