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]

The Free On-line Dictionary of Computing (19 January 2023):

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)