Someone who has power and influence in a field or activity; one who accomplishes tasks, who gets things done.
A person or organisation with a legitimate interest in a given situation, action or enterprise.
A person holding the stakes of bettors, with the responsibility of delivering the pot to the winner of the bet.
A person filing an interpleader action, such as a garnishee or trustee, who acknowledges possession of property that is owed to one or more of several other claimants.
An escrow agent or custodian.