Casablanca is one of the most revered and famous movies of all time.
But the only reason it got made was because of the passion of producer Hal Wallis. He had to fight the studio, he didn't get the director he wanted, he didn't get the lead actress he hoped for, the script didn't quite work, and even deep into the shooting, he didn't have an ending.
But Hal Wallis believed in the picture, and risked his reputation to save it.