persecutor (n.)

early 15c., persecutour, "one who pursues and harasses another unjustly and vexatiously," especially "a persecutor of Christians, an oppressor (of the Church or Christians)," from Anglo-French persecutour, Old French persecutor "persecutor, enemy" (12c., Modern French persécuteur) and directly from Latin persecutor, agent noun from persequi (see persecution).