Arthur (1981)

Charming but incessantly intoxicated multimillionaire Arthur Bach (Dudley Moore) stands on the brink of an arranged marriage to properly pedigreed heiress Susan Johnson (Jill Eikenberry), but his heart belongs to a working-class filcher (Liza Minnelli). When his family threatens to cut off Arthur's inheritance if he doesn't marry Susan, he asks loyal squire Hobson (John Gielgud, who chalked up an Oscar for his supporting role) to lend a hand.