Orson Welles
The man pushed cinema forward so far ahead with Citizen Kane that it still blows my mind. You could watch ten movies from the same year (or before it) and the vast difference between how modern Kane is and how old-fashioned everything else feels is insane.
Being blackballed from Hollywood couldn't stop him from remaining one of the most influential film makers of all time and as I always like to mention, he birthed the way modern battle scenes (Braveheart, Saving Private Ryan) were shot with Chimes At Midnight.