Drama, Historical, Musicals, Comedies (romantic, spoofs, slapstick), Westerns, War movies, Sci-fiction horror etc. A 60 year career, with 40 movies, 1 Television performance, about half a dozen theatre productions - so he had less than 50 outings to play just about every character in every possible genre.

He had his greatest success in dramas and which resulted in Brando redefining screen acting for ever. But he had gems in nearly every other genre which are the works of a genius
Have listed down my favourite movie from each genre.
Drama - On the Waterfront / The godfather. (depends on which side of the bed i get up from)
Historical - Mutiny on the Bounty (it really gets on my nerves that it gets unjustly criticized)
Musicals - Guys and Dolls (the only one he did, great one at that)
Comedies - The freshman (have already raved about it on every occasion possible)
Westerns - One Eyed Jacks (this movie hits u in the gut, always)
War movies - The young lions (vastly underrated classic despite being a huge hit)
Sci-fiction horror - The island of Dr. Moreau (probably his worst film ever).

SO Marlon Brando did it all, and did it his own way, and that way has never been traveled upon again by anyone...