This is a weird little movie, based on The Hunter, the first novel in the "Parker" series by Donald Westlake (writing as Richard Stark). Lee Marvin plays a renamed protagonist, Walker, who's been betrayed and shot by (respectively) his unfaithful wife and his unfaithful partner in crime after a successful heist.
This is an early John Boorman movie, and it has a lot of arty photography and a nightmarish feel. Dialog is (seems to me) intentionally unrealistic. And the plot is ludicrous. But it's a lot of fun to watch.
It's also interesting to compare this with a later movie version of the same novel, Payback with Mel Gibson. Mel's character is also renamed for some reason as Porter. Porter kills a pile of people on his way to retrieving his just deserts. Walker, on the other hand, kills nobody (something a lot of reviewers miss, I've noticed); people keep winding up dead, though. Porter winds up with his money and the girl; Walker winds up with nobody, and it's not clear whether he gets the money or not.