Vito Corleone (Marlon Brando) is on the cover, and on posters with the title. He is Godfather for a large amount of screen time. A significant element of the story is how large of a figure Vito is, and his shadow looms over Michael after becoming Godfather. Take into account Brando's huge career before that, and it makes sense for him to be considered the lead.
Anx1etyD0g t1_jda3xt7 wrote
Reply to comment by freedfg in TIL that Al Pacino boycotted the 45th academy awards in 1973, because despite having more screen time than Marlon Brando, he was nominated for best supporting actor and not best actor. by VengefulMight
Vito Corleone (Marlon Brando) is on the cover, and on posters with the title. He is Godfather for a large amount of screen time. A significant element of the story is how large of a figure Vito is, and his shadow looms over Michael after becoming Godfather. Take into account Brando's huge career before that, and it makes sense for him to be considered the lead.