Before there was hip hop, there was DJ Kool Herc.

On a hot day at the end of summer in 1973 Cindy Campbell threw a back-to-school party at a park in the South Bronx. Her brother, Clive Campbell, spun the records. He had a new way of playing the music to make the breaks—the musical interludes between verses—longer for dancing. He called himself DJ Kool Herc and this is When the Beat Was Born. From his childhood in Jamaica to his youth in the Bronx, here's how Kool Herc came to be a DJ, how kids in gangs stopped fighting in order to breakdance, and how the music he invented went on to define a culture and transform the world.