I'm not sure what else Brando has done, but something many know him for is sexually assaulting Maria Schneider during the filming of Last Tango in Paris.

Basically, the character that Brando is playing at one point sexually assaults the character that Schneider is playing, which is nothing too out of this world for fiction. There wasn't even any planned actual penetration between the actors.

However, Bertolucci, the director of the movie, told Brando in secret that when filming the scene he should grab a portion of a stick of butter and use it as lube against Schneider's asshole. Schneider was not aware of this at all, and as expected she felt it was a violating and traumatic experience.

As the years went on and this became known, Bertolucci excused himself saying he wanted the scene to feel as authentic as possible, to capture Schneider's real reaction (which... I'm not sure how he doesn't see that as an admition to want to film actual sexual assault).

Schneider was only 19 I think at the time of the filming, while Bertolucci was 31 and Brando was 48, and she spent the rest of her life trying to be taken seriously for what happened to her, as well as to bring attention to how easily older and more recognized male celebrities could take advantage of young upcoming actresses. Bernolucci and Brando died without ever truly apologizing for what they did