An agent is a person who acts on behalf of another person, or a representative of an agency.

• an FBI agent is an official representative of the Federal Bureau of Investigation.
• literary agent, a person who represents a writer
• sports agent, a professional who represents an athlete
• talent agent, a person who finds jobs for actors, models, and other people in various entertainment businesses.
• travel agent, a person who helps plan a trip and buys airline tickets and makes hotel reservations.

Agent can also mean:

• a secret agent, a spy (espionage)
• a free agent, a sports player who is out of contract
• a realtor (US), or real estate agent (Brit.)

In science:

• Agent Orange, a herbicide
• biological agent, an infectious disease that can be used in biological warfare

In fiction:

• Agents, characters in The Matrix
• Secret Agent, a 1936 film