To be directly involved in or concerned with a particular matter.

(bound form) used after a verb, adjective, or noun to represent the person or thing performing an action or possessing a quality; translates as "-er", "-ist", or "one who"

To be in charge of a matter; to be in control of a situation

(bound form) used after a verb, adjective, or noun to represent the person or thing performing an action or possessing a quality; translates as "-er", "-ist", or "one who"