oppressor (n.)

• arrogator
• autocrat
• bully
• caesar
• commissar
• czar
• despot
• dictator
• disciplinarian
• driver
• duce
• martinet
• oligarch
• overlord
• persecutor
• pharaoh
• scourge
• stickler
• taskmaster
• tormentor
• torturer
• tyrant
• usurper
• warlord