We have to start where hip hop started too: The Bronx. When block parties rose to prominence amongst the African American youth in the 1970s, the culture was born. DJs would cut a popular track's breaks to make way for a master of ceremony to kick a few rhymes, in a similar way that the Jamaicans used to do it (in Jamaica, they call it toasting).
The Bronx is credited with producing these essential artists, among others:
Grandmaster Caz, Melle Mel, Busy Bee, Afrika Bambaataa, Grand Wizard Theodore and the Fantastic Five, Treacherous Three, Slick Rick, CL Smooth, Kurtis Blow, KRS One, Inspectah Deck, Canibus, Camp Lo, Lord Finesse, Big Pun, Fat Joe, Grandmaster Flash, Hell Rell, and Kool Keith.