In a qui tam action, a private party called a relator brings an action on the government's behalf. The government, not the relator, is considered the real plaintiff. If the government succeeds, the relator receives a share of the award. Also called a popular action.
For example, the federal False Claims Act authorizes qui tam actions against parties who have defrauded the federal government. 31 U.S.C. § 3279 et seq. If successful, a relator in a False Claims Act qui tam action may receive up to 30% of the government's award.
Intervention (the government may intervene in a qui tam action)