Bob Marley.
He helped create, define, and refine an entire genre of music. When most (if not all) people think of reggae, he's the first person that comes top mind. I cannot think of another genre that has such a singular figure that people agree upon. Classical, jazz, blues, rock, country, folk, etc. ...so many eras, sub genres, off-shoots, and varieties, but few undisputed faces/leaders.
He never shied from singing about his beliefs, especially political beliefs. Despite his association with pot in the U.S., he is the music of revolution throughout much of world. Who else can say that? Maybe a handful of other artists/bands, if any. Bob Marley is music, poetry, politics, revolution, evolution, and more. His music moves listeners in so many different ways. A true artist. A true genius.
I'm tired...me go sleepy now.