Final answer:
Elvis Presley fundamentally changed the world of R&B by blending blues and country, creating a new genre known as rock 'n' roll. His first record demonstrated this unique mix of styles and led to his monumental success, affecting the evolution of American music.
Step-by-step explanation:
The artist who changed the world of R&B by mixing together blues and country is Elvis Presley. Presley, a native of Mississippi and Tennessee, was influenced by multiple music genres, including gospel, blues, bluegrass, country, western, and R&B, and successfully merged them to create what would become known as rock 'n' roll. His initial recordings at Sun Records, such as "That's All Right" and "Blue Moon of Kentucky," demonstrated this blend of styles. Presley's unique contribution to music came from his ability to bridge these diverse sounds, which catapulted his songs to the top of R&B, country, and pop charts, and made rock 'n' roll resonate with a wide audience.
Elvis's blend of music genres represents the cultural shift in American music during the mid-20th century, where the combination of electric instruments with the sounds of gospel, blues, country, jazz, and R&B gave birth to the new sound of rock and roll. His song/guitar style, as well as his stage presence, had a profound impact on future generations of musicians and transformed American music forever.