The team agent is the person with the developer account Team Agent role who is responsible for entering into legal agreements with Apple, including app transfer agreements. The Team Agent role also includes the privileges of all other roles in the developer account.
The person who enrolls in the Apple Developer Program or Apple Developer Enterprise Program is automatically assigned the Team Agent role, given an iTunes Connect account for the organization, and in iTunes Connect, assigned the Legal role. There can only be one team agent but the role can be transferred to another person.
If you enroll as an organization, you can invite others to join the team and assign program roles that restrict the tasks others can do. If you enroll as an individual, you are the team agent for a one-person team. In iTunes Connect, you can add users and assign roles whether you are enrolled as an individual or an organization.
To understand what a team agent and others can do, go to Program Roles and iTunes Connect Roles.