Preacher Rap
One of the main factors in the evolution of rap music were the early "straining preachers", many of whom recorded to extraordinary popularity in the 1920s and '30s. Rev. J.M. Gatescould belt out a sermon and sometimes a short hymn in that time, usually joined in the singing by a few members of his church. The rhythmic exhortations of preachers such as Gates were the predecessors for the secular rhymebusters of the 1970s. Back then, Gates had a superstar status and his funeral was the largest held in Atlanta before Martin Luther King's.
Source: All about blues music, Cross rhythms, Wikipedia
Source image: Wikipedia