An Actor in the context of a use case is a person or thing that interacts with or performs an identified task. It could be a user or another system.  An actor represents a role played by an external person, process or a thing interacting with a system. An actor is not a description of a job function.

A given role should reflect a unique function performed by one or more persons in an institution.  Roles are not job titles, since job titles are institution-specific.  In some institutions, one person may perform only one role; in others, the person may perform more than one role.  Each role should be aligned with the specific objectives or purpose of individual business functions.  In other words, roles should be identified in consideration of business objectives and within the context of a discrete business activity, not based on which person performs the activity.

Example actors include: 

Performer

Role: Responsible for carrying out various actions or activities. 

Planner

Responsible for initiating various actions or activities. 

Reviewer/Confirmer

Responsible for ensuring that various data that have been entered into the system are factual. 

Manager