Alec Guinness as Gulley Jimson

This was a really good movie, and I though Alec Guinness really was amazing. The only movie of his I'd seen was Star Wars, and let's face it, he was pretty subdued in that one.
I am curious about the character of Gully Jimson. Who was the inspiration? I know an old guy that is very much like him, with a much vulgar lexicon though.