I've also heard people make the joke, "He's not a has-been, he's a never-was."
A has-been is a common term for someone who was famous but no longer is popular, or is no longer getting roles.
A never-was is not a common term, but it would be someone who aspired to be an actor but never had success.
A will-be is not a common term either, but it would be someone who aspires to be an actor and who has not yet had success, but who is going to be successful in the future.
I have no idea whether the Lauren Bacall quote is true.