As far as appearance, if that were a significance, I would choose Nick Nolte:
He certainly has an intensity, but I'm not sure that kind of intensity would work with a possible movie (Whether it's in the works or not, I don't know).
I would choose Richard Dreyfuss or Robin Williams. They would/add humor to the movie, and they both are good at personally driven
roles. They're both good at playing the role of someone with a purpose.