He didn't turn down "The Godfather."
Brando, who hated Reynolds with a passion, said that if Reynolds came on the picture to play Michael, then he (Brando) was off the project.
It seems that Reynolds had done a barely-veiled parody of Brando in a Twilight Zone episode. (The Bard) Naturally, thin-skinned, egotistical, Brando took offense.
Clips of Reynolds playing this part are available on youTube.
See: Rocky Rhodes
Brando thought the whole world revolved around him.
Too bad.
He could have been somebody.................