In his biography, Christopher Frayling called him 'the first post-modern film maker', and as such Sergio Leone has had an arguably underrated and largely overlooked influence on Star Wars . A lengthy discussion of Leone's approach to film making, and how a samurai became a cowboy who became a bounty hunter in a galaxy far, far away.
WWII was an enormous influence on all kids of the 50s and 60s, and Lucas was no exception. From the general good vs evil nature of the conflict to the specifics of war epics like The Guns of Navarone and air-heroics of The Dam Busters and 633 Squadron, it seems entirely possible that Star Wars would never have existed if not for the war.
With a career stretching almost 60 years, Akira Kurosawa remains one of the most influential directors in the history of the medium. The pinnacle of his popularity however was perfectly timed with a batch of impressionable USC students ready to take on the world, and his impact on George Lucas in particular is the stuff of legends.