Actor

Lat. The party who institutes or prosecutes an action. In some actions, as in replevin, the term is extended also to the other party. Actor in rem suam: an agent in his own matter. Actor qui contra regulam quid adduxit non est audiendus: a pleader ought not to be heard who advances a proposition contrary to the rules of law. Actor sequitur formam rei: the plaintiff follows the form of proceeding. Actor sequitur forum rei: the plaintiff follows the forum of the thing; the plaintiff follows the court of the defendant. Actori incumbit probatio [onus probandi], Lat. The burden of proof lies on the plaintiff.