Nirvana is often credited with killing the "hair" bands common in the late 1980's.  Personally, I think while their influence was decisive it is also a little overestimated.  For one thing, we forget the impact that Pearl Jam's first album had at the time.  For another Guns `N' Roses first album was really the death knell to the pretty "New York Dolls" wannabes.  "Welcome To The Jungle" breathed fire and just laid everyone on their butts.  It was like riding a Harley-Davidson compared to a moped.  This was how hard rock was done and it had more red blood in its whiskey soaked veins than any band out there.