Agent

An agent is the conscious and deliberate instigator of an action. For example, Alice is an agent in each of the following sentences:

Alice sipped her coffee.
Alice slapped Peter.
Alice sang a song.
Alice wrote a book.

In a passive sentence, the agent is the expression that says who or what an action is done by.

• A book was written by Alice (agent).
• This picture was probably painted by a child (agent).