ACTOR

actor. 1. One who acts; a person  whose  conduct is in question. 2.Archaic. A  male  plaintiff.

3.Hist. An advocate or pleader; one who acted for another in legal matters. Cf. REUS(1).4.Roman

law.  (ital.)  A  person  who  sues;  a  claimant.  —  Also  termed  (in  sense  4)  petitor.  Pl.  (in  sense  4)

actores.[Blacks Law 8th]