The Actors that don’t really act thread got me thinking . . . many of the actors mentioned there do have a wide range, like Jim Carrey, but what I think people are picking up on are common denominators in all their performances that must go to something inherent in the real guy or gal. FWIW, I don’t know anything about his personal life, but going by his performances I think the real Jim Carrey must have a deep well of anger and hurt that I can see fueling his acting in a range from manic comedian to quiet troubled guy.
Something about his over the top characters tells me that Samuel L. Jackson is really shy in real life.
I’m racking my brains for other examples, but my impressions may be tainted by things I’ve heard in the news; e.g., Steve Buscemi striking me as a humble, down-to-earth guy, or Morgan Freeman giving me just a hint of a dirty old man vibe.