System user
A system user is a business-owned login that is not a person.
With a system user, the agent gets a dedicated login your brand owns. The change history, the platform's record of each edit and who made it, then shows the agent and not a buyer. Without one, every tool request to a connector such as Google's runs under the signed-in person's identity. An agent will try any tool its login reaches, so a system user gets the narrowest role that does its job, read-only to start.
The dedicated login matters most for scheduled tasks, which the AI assistant runs on its own at set times. A scheduled task can use every tool of each connector it includes, writes too, without asking for permission during a run, and its connector actions appear as the signed-in user.
Example
On Meta, a brand can sign its agent in as a system user. Meta's connector accepts one, though not one with the admin role, and to start read-only, grant ads_read rather than ads_management.