Agent

agent comes from ag- meaning"to do" plus the Latin suffix -ent which means "a person who." Thus, agent means "a person who does something." This word is applied to someone who does a specific action or job, or who works for or represents an individual, company, or government bureau.

He is an FBI agent.
Does the actor have a press agent?
Does that company have a sales agent in our town?

A word based on agent is agency, meaning "a company, department or bureau that does a specific job or that represents other people or companies."

She works for an employment agency.