term:

Relator

relator n

: a party other than the plaintiff upon whose information, knowledge, or relation of facts an action is brought when the right to bring the action is vested in another: as
a : the private person who brings a qui tam action
b : a party who has standing and on whose behalf a writ (as of mandamus) is petitioned for by the state as plaintiff [ then filed…a petition in prohibition requesting this court to prohibit respondents from transferring the funds "State ex rel. Tate v. Turner, 789 S.W.2d 240 (1990)"] see also ex relatione

Source: Merriam-Webster's Dictionary of Law ©1996. Merriam-Webster, Incorporated. Published under license with Merriam-Webster, Incorporated.