A relator is a private individual or body who seeks to have court proceedings brought in a Law Officer’s name to vindicate a public right where no private cause of action or standing exists. If satisfied the complaint raises a genuine matter of public interest, the Attorney General (England and Wales and Northern Ireland) or the Lord Advocate (Scotland) may grant consent (often called the Attorney General’s fiat). The case is then issued as, for example, Attorney General ex rel [Relator] v [Defendant].
This is a case law term, not a statutory definition. Typical relator actions include proceedings to restrain a public nuisance, enforce charitable trusts, or challenge ultra vires conduct affecting public rights. The Law Officer retains control and discretion over the claim, while the relator supplies evidence and usually gives an indemnity or undertaking as to costs.
In England and Wales and Northern Ireland, modern judicial review largely replaces relator actions for public law challenges, but they remain relevant in charity and public nuisance contexts. In Scotland, similar principles apply via the Lord Advocate. In Ireland, comparable ex relatione proceedings exist through the Attorney General, recognised in case law. Usage is broadly consistent across these jurisdictions.