Complex sentence: Coppola had feared Brando might be too young to play the Don but was electrified by the actor's characterization as the head of a crime family, but he had to fight the studio in order to cast the temperamental actor.
Split into simpler sentences: Coppola had feared Brando might be too young to play the Don but was electrified by the actor's characterization as the head of a crime family. Even so, he had to fight the studio in order to cast the temperamental actor.