Nirvana is the creators of what we like to call grundge. Kurt Cobain and his dark and morbid lyrics had seperated this band mostly from the rest, which was hair metal at the time. Also their style of creating music was entirely different, they didn't make riffs but instead just used a certain few chords in different progressions. Nirvana is one of the most influential and time held bands and will always be recognized as the forfronters of what music had become in the ninties. Go out and pick up one of their records and jam out to it and tear it up.