Marlon Brando was arguably the greatest actor the world has known. After watching Listen to Me Marlon, it's easy to see why he's thought of as the best. This film is fascinating - a documentary telling his life story in his own words - via tapes he recorded throughout his lifetime. He made Method Acting (the Stanislavsky Method) famous with his teacher Stella Adler.
I recently watched the first two Godfather movies, On the Waterfront and Last Tango in Paris - some of Brando's greatest work in film. It was a great experience to revisit these films anew after having seen the documentary.
Marlon was also quite an activist and advocated for the rights of black people when it was very unpopular to do so... as well as American Indians. He was so utterly human - through and through - which is what made him such a great actor: his intense empathy for humanity.
Here is a drawing of Brando playing Stanley Kowalski in A Streetcar Named Desire... I did when I was about 18: