In an agency situation, at least three persons are involved: a principal, an agent, and a third party.
The principal is the person who wants to enter into one or more legal transactions, and who empowers another person to act on their behalf in bringing those transactions about.
The agent is the person who is appointed and empowered by the principal to represent the principal in the carrying out of one or more legal transactions on behalf of the principal.
The third party is the person with whom the agent deals on behalf of the principal.