relator

1. One who relates or narrates: a relator of stories for children.
2. Law. A beneficially interested person on whose behalf an action is maintained by a sovereign power or a state.

The individual in whose name a legal action is brought by a state; the individual who relates the facts on which an action is based.

The relator is the individual upon whose complaint certain writs are issued. The relator is the party of interest in a proceeding, who is allowed to institute such proceeding in the name of the people, or in the name of the attorney general when such official has the sole right to sue. For example, if A was the relator and B was the defendant, the citation of the case would read, State ex rel. A v. B.