Complainant /(kŏm*plān"ant)/

Com·plain·ant

Complainant

n.
  1. One who makes complaint.
    Eager complainants of the dispute.
    — Collier.
  2. One who commences a legal process by a complaint. (Law)
    He shall forfeit one moiety to the use of the town, and the other moiety to the use of the complainant.