Underground Hip-Hop is the reason everyone gives you a dirty look when you say Rap isn't music.
Hip-Hop as a music arose in the late 1970's, spread throughout the (at the time) almost exclusively black culture it came out of through block parties in New York, specifically the Bronx. It developed as a party music, created by DJ's who extended the common percussion/instrumental "breaks" in many funk/soul/reggae/dub songs to longer lengths, allowing those more dance-able excerpts to dominate the shindig. DJ Kool Herc is widely regarded as the "godfather" of hip-hop, and pioneered many of these techniques. Gradually, DJ's began "toasting" over the extended instrumentals, adding the "rap" the hip-hop culture. This is widely regarded as being the last important or interesting thing to happen in the Bronx.
All hip-hop was underground until the rise of Run-DMC in the late 80's. However, this early period isn't referred to as "underground hip-hop"- it's often simply called "that old school shit" (shit being used in the positive sense). That old school shit is the only music that underground hip-hop artists can admit to enjoying, besides esoteric experimental shit (shit being used in the negative sense). Hip-Hop music post-1993 is derivative, overly popular, pointlessly misogynistic music that doesn't keep it real. Except for the Wu-Tang Clan. From what I understand, they are not to be fucked with.
From here things get vague and often tedious, with approximately five thousand different groups and solo artists claiming to be the most important act in underground hip-hop. Ask any white college student, and they'll give you their take on the best "back-packer" hip-hop artist. The following section will give you a run down on some of the most widely agreed to not suck.
Presented here in alphabetical order:
Widely known for his impenetrable literary lyrics that (realistically) often make no goddamned sense. He released his first two full length demo recordings on CD-R, and has refused to re-release them. What a dick.
Important for combining hip-hop and emo music. What a dick.
Utterly insane, even for underground hip-hop. Known for rapping to the melody, and having approximately nine hundred different voices he raps in, about five of which aren't annoying. When not rapping about imaginary real estate, ashanti masks, furry threesomes, and baby vomit (his lyrics will be discussed in the next section), he talks about how much he hates his main demographic, white college students. You make me feel guilty for being white and liking hip-hop, Busdriver. What a dick.
Known for having their best song in a Tony Hawk soundtrack. What dicks.
Renowned for having some of the most abrasive, harsh, downright scary music in all of hip-hop, and for being the first outlet of El-P. Known by me as the group that wrote the most terrifying song about domestic abuse in the history of music, that often causes me to curl up into a ball beneath my bed. What dicks.
A project of Kool Keith, known for being insane in the most awesome ways possible. The album released under the pseudonym is called Dr.Octagonecologyst, and is a concept album about an alien who pretends to be a gynecologist to molest women. I am in no way joking, it's fucking incredible. Unfortunately, this is the only time Kool Keith let himself be completely insane, and none of his other albums have reached the heights he did in this album. What a dick.
Famous as both a tremendous producer and rapper, he reminds me a lot of R.E.M., as they've both made some of the most acclaimed records of the last 30 years, but I just can't get through a whole album of either one. What a dick.
Put the "hard" in hardcore rap. But not in the way most try to be hardcore- ESham stakes a darker territory. How you ask? He has an album titled "KKKill The Fetus". Unfortunately, the Insane Clown Posse cites him as an influence. Although that's not his fault, still: What a dick.
A member of the Wu-Tang Clan, who created one of the best records of all time in "Liquid Swords". Unfortunately, he is too popular to be underground. What a dick.
One of the longest lasting and most important crews in underground hip-hop. Their song "A Day At The Races" is the musical equivalent of a speedball. It's also been featured in every skateboard video ever. What dicks.
Known for having an album that I have yet to listen to, but is widely hailed as a masterpiece. By Pitchfork. What dicks.
I'll be honest, I haven't listened to their album yet. But everyone seems to love them.
I'm a dick.
One of the first groups to pioneer live instrumentation, often drawing genre tags such as "jazz-rap". I have all their albums, and cannot listen to any of them all the way through. They're good, but shit, I've never heard so many throw away tracks since the last Pavement album I listened to. What dicks.
Pretty damn good indie rap. Unfortunately, that question mark is part of the name. What dicks.
Underground Hip-Hop is often seen as a reaction to the increasingly glorified street violence and womanizing seen in the rise of gangsta rap. This was seen as a move away from credibility and artistry, and was not keeping it real. Seeing as the most important aspect of hip-hop culture is the harnessing of realness, underground decided to move away from the unreal street fantasies gangsta rap popularized, and rapped about casting agents, cowgirls, the bottle neck effect as it relates to human population, and the church of the operating room. Much more real.
Common lyrical inspiration for underground rappers
One legendary pioneer in the realm of batshit insane is Busdriver. Abstract beyond abstract, it often seems as if he rambles the first thing that comes into his mind that happens to rhyme, regardless of actual meaning. He is allowed to get away with this because the things he comes up with are absolutely, certifiably awesome. Some examples:
"Now during these hours this Ashanti mask is my body cast holding together these withered bones"
"This abused child was conceived on a swivel chair by three strangers dressed like three little bears with mommy's cervix as a major."
"I'm a big lonely teddy bear who occupies empty air. I'm not a millionaire I'm a pennyaire, yes!"
"Go back to Compton you dirty Nigger we don't sell watermelon here is what I yell at the white folk on the way to the gun show once a year"
I could go on for hours.