Persecutor (noun)

1. A person who persecutes or oppresses others, especially for reasons of race, religion, or political beliefs.
2. Someone who harasses, mistreats or oppresses others.

Origin:

From latin persequi "to pursue, follow", from per- "thoroughly" + sequi "to follow".

Examples:

1. The dictator was a ruthless persecutor of political opponents.
2. He was a known persecutor of religious minorities.
3. During the war, the invading army was the main persecutor of the civilians.
4. The company's CEO was a notorious persecutor of employees who disagreed with him.
5. She became a victim of persecution by her classmates.