The Collaborative International Dictionary of English v.0.48:

Initiator \In*i"ti*a`tor\, n. [L.]
   One who initiates.
   [1913 Webster]

WordNet (r) 3.0 (2006):

initiator
    n 1: a person who initiates a course of action [syn:
         instigator, initiator]

Moby Thesaurus II by Grady Ward, 1.0:

50 Moby Thesaurus words for "initiator":
   ancestors, apprentice, architect, artificer, artist, author,
   begetter, beginner, builder, conceiver, constructor, craftsman,
   creator, designer, deviser, discoverer, effector, engenderer,
   engineer, executor, executrix, father, founder, generator, grower,
   inaugurator, industrialist, instigator, institutor, introducer,
   inventor, journeyman, maker, manufacturer, master,
   master craftsman, mother, organizer, originator, past master,
   planner, precursor, prime mover, producer, raiser, realizer,
   shaper, sire, smith, wright



The Free On-line Dictionary of Computing (30 December 2018):

SCSI initiator
initiator

    A device that begins a SCSI transaction by
   issuing a command to another device (the SCSI target),
   giving it a task to perform.  Typically a SCSI host adapter is
   the initiator but targets may also become initiators.

   (1999-02-10)