They draw you into the film and build an emotional, if not moving, link between you and the screen. There are little subtleties in their behavior that you think only you have keyed into. They may not be the main character but often times overshadow the other roles. In short, they're the actors that make you forget you're watching a movie.
I personally think River Phoenix always did a very impressive job with his roles, Even though I've only seen him in a few movies, he always stands out in my mind.

That's him in "My Own Private Idaho". But I first saw him in "Stand by Me" when he was wee lad.

So share your favourite actors/actresses and we will
discuss...