Final answer:
Charley Pride was the African American artist who aimed to appeal to a country audience by blending country and rhythm. His success in the predominantly White genre of country music helped break racial barriers, similar to the effects of rock 'n' roll pioneers like Elvis Presley.
Step-by-step explanation:
The African American artist who set out to appeal principally to a country audience with the synthesis of country and rhythm was Charley Pride. Unlike Jimi Hendrix whose genre is primarily associated with rock and psychedelic music, or Johnny Cash who was predominantly a country music star with a distinct style, Charley Pride ventured into the realm of country music at a time when it was largely dominated by White artists. His success in this genre was significant as it broke racial barriers, much like how rock and roll artists like Elvis Presley rose to stardom and helped to break down color barriers by incorporating African American musical motifs into their mainstream music.