noun
A person who participates in a rebellion or uprising against authority.
反乱者たちは城を占拠した。
The rebels occupied the castle.
政府は反乱者を鎮圧するために軍隊を派遣した。
The government dispatched troops to suppress the insurgents.
Compound of 反乱 (rebellion) + 者 (person). The kanji 反 means 'anti-' or 'oppose', 乱 means 'disorder' or 'revolt', and 者 is a common suffix for 'person'.