When Brando arrived for filming in the Philippines in September 1976, he claimed he was dissatisfied with the script; Brando didn't understand why Kurtz was meant to be very thin and bald, or why the character's name was Kurtz and not something like Leighley. He claimed, American generals don't have those kinds of names. They have flowery names, from the South. I want to be 'Colonel Leighley'. And so, for a time the name was changed under his demand.
When Brando showed up for filming he had put on about 40 lbs and forced Coppola to shoot him above the waist, making it appear that Kurtz was a 6-foot 6-inch giant.
Many of Brando's speeches were ad-libbed, with Coppola filming hours of footage of these monologues and then cutting them down to the most interesting parts.