actor

noun

1. (obsolete)Someone who institutes a legal suit; a plaintiff or complainant.
2. (obsolete)Someone acting on behalf of someone else; a guardian.
3. Someone or something that takes part in some action; a doer, an agent.

   “A man may be principal in an offence in two degrees. A principal, in the first degree, is he that is the actor, or absolute perpetrator of the crime; and, in the second degree, he who is present, aiding, and abetting the fact to be done.”

   “Never, my dear Bethel, did the most feverish dreams of fiction produce scenes more painful, or more terrific, than the real events to which I have been an actor, since the date of my last letter.”

   “Mr. Clay had been too prominent an actor in public affairs to allow whig deception and misrepresentation a fair opportunity for successful action.”

4. A person who acts a part in a theatrical play or (later) in film or television; a dramatic performer.

   “Seems like everyone's an actor / Or they're an actor's best friend / I wonder what was wrong to begin with / That they should all have to pretend”

   “Exactly. Marijuana is something we just all gradually decided is okay, like Mark Wahlberg as a serious actor. “You know what? Sure, I’ve decided I’m fine with that.””

   “"I'm an actress -- actor, as we have to say these days."”

5. (Ancient-Rome, obsolete)An advocate or proctor in civil courts or causes.
6. The subject performing the action of a verb.
7. The entity that performs a role (in use case analysis).