persecutor n.

mid-14c., persecucioun, "oppression for the holding of a belief or opinion," from Old French persecucion "persecution, damage, affliction, suffering" (12c.) and directly from Latin persecutionem (nominative persecutio), noun of action from past-participle stem of persequi "to follow, pursue, hunt down; proceed against, prosecute, start a legal action," from per "through" (from PIE root *per- (1) "forward," hence "through") + sequi "follow" (from PIE root *sekw- (1) "to follow").

General senses of "malevolent oppression, harassing or oppressive treatment," also "a time of general or systematic oppression" are from late 14c. Psychological persecution complex in reference to an irrational sense of being victimized by malign forces as a feature of a mental disorder is recorded from 1961; the earlier phrase for it was persecution mania (1892).