Refers to a person who secretly plans something harmful or illegal with others.
彼はクーデターの陰謀者として逮捕された。
He was arrested as a conspirator in the coup d'état.
陰謀者たちは密かに会合を開いた。
The conspirators held a secret meeting.
Compound of 陰謀 (plot, conspiracy) and 者 (person).