Short answers, pulled from the story.
Rock and roll did not acquire its name as a genre until 1954, though its early elements can be heard in blues records from the 1920s and country records from the 1930s. Cleveland disc jockey Alan Freed had been using the term on his mainstream radio program since 1951 to describe the music style.
Rock and roll drew primarily from rhythm and blues, with additional influences from gospel, jazz, boogie-woogie, electric blues, jump blues, swing, and folk music. In its earliest form, either the piano or saxophone was the lead instrument, later replaced by the electric guitar.
Bill Haley and His Comets' "Crazy Man, Crazy" is recognized as the first rock and roll song to reach the mainstream charts, peaking at number 15 on the Billboard singles chart in May 1953. The song notably features guitar fills in place of piano or saxophone.
G. C. Altschuler noted that rock and roll had a positive influence on the civil rights movement because of its widespread appeal to both Black American and White American teenagers. M. T. Bertrand observed that many people at the time saw the music as encouraging racial cooperation and shared experience across segregation lines.
A series of events between 1957 and 1960 effectively ended the first wave: Little Richard retired in October 1957, Elvis Presley entered the Army in March 1958, Buddy Holly died in a plane crash in February 1959, and the Payola scandal implicated Alan Freed in November 1959, among other disruptions. The rawer sound of early rock and roll was commercially superseded by a more polished, image-driven pop style.
White pop artists frequently recorded cover versions of Black rhythm and blues songs because labels aimed at white audiences had far better distribution networks. Pat Boone recorded sanitized covers of songs by Fats Domino, Little Richard, the Flamingos, and Ivory Joe Hunter. The practice was legally simple due to the compulsory license provision of United States copyright law.