Haile Salassie was known as "Ras Tafari" before he became emperor of Ethiopia. He was a master diplomat who managed to keep Ethiopia the only African nation free from colonization. Jamaicans got all mad obsessed with him, because keeping whitey out of your land was pretty rad when the rest of Africa was under European rule. So these Jamaicans started a religion (or a Christian cult really... with lots of pot smoking thrown in for good measure) based on him, basically elevating him to something more than human.
Apparently he was a prick to the Ethiopians though, as most dictators tend to be, so they deposed him in 1974 and someone murdered him a year later. Naturally, the Ethiopians are a little weary of the Rastafarians, who have a habit of making pilgrimages to Ethiopia, which they call their promised land.