The Collaborative International Dictionary of English v.0.48:

Persecutor \Per"se*cu`tor\, n. [L.: cf. F. pers['e]cuteur.]
   One who persecutes, or harasses. --Shak.
   [1913 Webster]

WordNet (r) 3.0 (2006):

persecutor
    n 1: someone who torments [syn: tormentor, tormenter,
         persecutor]