Bill Murray, seen in the still above as the epic Carl Spackler in Caddyshack, was not exactly a powerhouse in the film comedy world in the 70's, but he was getting there. Murray wrote for and acted in SNL in the 70's, and his iconic importance in Caddyshack (which also stars Rodney Dangerfield and Chevy Chase) is evidenced by a Caddyshack fansite: CarlSpackler.com, a hilarious (if low-tech by today's standards) homage to the film.
Interestingly, Murray's role, back in 1980, might not have been entirely far-fetched. A "Production Information" document from the same fansite reveals that Murray's brother (Brian Doyle-Murray) wrote the screenplay, and was inspired by his own work as a caddy at a golf course as a teen, where Bill Murray also worked as a groundskeeper. Well I'll be damned if that's not an eerie possibility, that his character may have been close to psychological truth.
A good, biased synopsis of his career, found here, states that Caddyshack probably was his best film, and still is, but what about Ghostbusters? His more serious roles are still frequently comedic, and his increasing ability as a more mature actor to combine psychological depth and comedy sets him apart from a lot of other SNL alumni.