The four different periods of hip-hop each had a different sound; 2000s-era hip-hop artists draw on all of these different styles to create their music.
Roots hip-hop (1975-1978) was developed by Black DJs in New York City who played funk and soul music at block parties. To entertain the crowd, DJs began adding in percussion breaks from other records by using a second turntable and an audio mixer. Important roots hip-hop artists included DJ Kool Herc and Grandmaster Flash.
Old School hip-hop (1979-1985) arose when the DJs and MCs at block parties began to introduce the mixes of dance music they were playing by using microphones. Using a rhythmic, rhyming vocal style called "rapping," DJs would speak over their percussive backing tracks. Often, this rapping would consist of boastful claims about their mixing prowess, and a dismissive downplaying of the skills of rival DJs.
Golden age hip-hop (1986-1996) developed when a new generation of rap artists and rap groups such as Run-DMC began to raise the bar for the complexity of rhyming and wordplay. In the late 1980s, Ice-T and a group called N.W.A. introduced a subgenre called "Gangsta rap" which featured sexually-explicit lyrics and references to drugs, weapons, and gangs.
Another subgenre called Miami Bass, exemplified by the group 2 Live Crew, had bass-heavy songs with sexually-themed lyrics. The Golden Age came to an end in the mid- to -late 1990s, after several well-known rappers such as Tupac Shakur and the Notorious B.I.G. were shot to death.
Current hip-hop (1997-present), sometimes called "New School" hip-hop became a mainstream form of pop music. The best-selling hip-hop artists and producers became wealthy celebrities, which in turn spawned a subgenre called "bling," which emphasized the trappings of success: expensive jewellery; premium cognac and champagne; and fine cars.
When hip-hop became a mainstream genre, some artists from other genres began incorporating hip-hop elements. Pop music began to use hip-hop style percussion tracks. Soul music was merged with hip-hop to create neo-soul, and metal merged with hip-hop to create a new style exemplified by Linkin Park.
50 Cent for 1.
-----------------------------------------------------------------------------------------
The above content does not adequately answer the question, so here are some ACTUAL genres of hip-hop/rap:
Gangsta Hip-Hop
East Coast Hip-Hop
West Coast Hip-Hop
Boom-Bap Hip-Hop
Backpack Hip-Hop
Deep South Hip-Hop
Horrorcore Hip-Hop
Skateboard Hip-Hop
Surf Guitar Hip-Hop
Nerdcore Hip-Hop
Jazz Hip-Hop
Battle Hip-Hop
Club Banger/Dance Hip-Hop
Etc...
...many more are bound to be discovered because of the infinite innovative potential of artists in the hip-hop/rap fields. Anyone can be an artist and change the genre, and no where is this more prevalent than in hip-hop/rap.