Agent

Agent, in grammar, is the word which denotes someone or something as the doer of an action. It refers to the cause or initiator of an event rather than the subject of a verb. It is determined through its relationship to the action expressed by the verb. Thus, an agent is the subject of an active verb in active voice, or of a passive verb in passive voice.

An agent noun typically contains er or or, such as runner, or accelerator.

It should not be confused with a subject, since a subject is determined by order of words in a sentence, not by the meaning of the word as doer of an action or any such relationship with the action of the verb.