When rock music ― first known as rock ’n’ roll ― first appeared on US dance floors in the late 1940s, it was not considered rebellious due to its more aggressive sound. In fact, compared to its later development, early rock music was fairly tame. (Watch Bill Haley performing Rock Around the Clock in 1954 ― a song that is widely considered to have brought rock music into the mainstream ― and you might be surprised.)