Persuasive writer is probably Frantz Fanon imo, this guy was a genius, if you ever read Wretched of the Earth, Black Skin White Mask you would understand what I'm talking about. Another take would be Edward Said (R.I.P.), the way he wrote was just thought provoking, try to get your hands on Orientalism and you'll see for yourself.
As for speaker there is Malcolm X, Nelson Mandela or Gandhi. I never saw in my whole life somebody make 800+ million people move their minds by an intelligible speaker as Gandhi. We do also have to note that Mandela is a great and a courageous person who fought for what he believed and is blindly praised in the whole world up to this day.
Peace