"Yojimbo" by Akira Korosawa and "A Fistful Of Dollars" by Sergio Leone.
...Kurosawa wrote Leone a letter: 'You made a very good movie, but it's not your movie.' Leone's response was: 'Omg, I got a letter from Kurosawa!!' Rather than realizing he was in for some legal problems....Anyway. Both movies were masterpieces. Yojimbo was based on a Dashiell Hammett novella called "Red Harvest", according to a few scholars, in which the protagonist was a depression era thug in a gangster war in a western town.