Someone or something that takes part in some action; a doer, an agent.
The entity that performs a role (in use case analysis).
A person who acts a part in a theatrical play or (later) in film or television; a dramatic performer.
The subject performing the action of a verb.
An agent entrusted with the possession of goods to be sold in the agent's name.
A merchant earning a commission by selling goods belonging to others.
A person entrusted with a confidential task, often secretly to place a bet.