The difference between Agent and Undergoer

Agent as a noun:

One who exerts power, or has the power to act

Agent as a noun:

One who acts for, or in the place of, another (the principal), by authority from him/her; someone entrusted to do the business of another

Agent as a noun:

A person who looks for work for another person

Agent as a noun:

Someone who works for an intelligence agency

Agent as a noun:

An active power or cause or substance; something which has the power to produce an effect

Agent as a noun (computing):

In the client-server model, the part of the system that performs information preparation and exchange on behalf of a client or server. Especially in the phrase “intelligent agent” it implies some kind of autonomous process which can communicate with other agents to perform some collective task on behalf of one or more humans.

Agent as a noun (grammar):

The participant of a situation that carries out the action in this situation, e.g. "the boy" in the sentences "The boy kicked the ball" and "The ball was kicked by the boy".

Undergoer as a noun:

One that undergoes.