An actor is at his best a ...

An actor is at his best a kind of unfrocked priest who, for an hour or two, can call on heaven and hell to mesmerize a group of innocents.
 Alec Guinness

Quotes from the same author

An actor is totally vulnerable. His total personality is exposed to critical judgment - his intellect, his bearing, his diction, his whole appearance. In short, his ego.
 Alec Guinness