An actor represents a role of a user that interacts with the system that you are modeling. The user can be a human user, an organization, a machine, or another external system.
You can represent multiple users with a single actor and a single user can have the role of multiple actors. Actors are external to the system. They can initiate the behavior described in the use case or be acted upon by the use case. and exchange data with the system.
In models that depict businesses, actors represent the types of individuals and machines that interact with a business. In models that depict software applications, actors represent the types of individuals, external systems, or machines that interact with the system.
You would typically use actors in use case diagrams, but you can also use them in class and sequence diagrams.
As the following figure illustrates, an actor is displayed as a line drawing of a person.
Each actor has a unique name that describes the role of the user who interacts with the system.
You can add documentation that defines what the actor does and how the actor interacts with the system.