Metallica
They saved heavy metal and have influenced virtually every metal/hard rock band after them. They also took metal in a new direction. They have ridiculously fast tempos, harmonized guitars and almost-10-minute instrumentals that don't get boring. Who else is talented enough to play instrumentals that people want to hear?
They've always played what they felt (true meaning of music) and broke through all sorts of barriers. James' lyrics are more diverse than any other and could be promoted as poetry. Kirk's solos are massively complicated and amazing, as is the way Kirk's and James' guitars seem to speak to each other. And Metallica is still relevant today, going on 30 years (unlike the friggin Rolling Stones who only play that annoying Satisfaction song).
The true measure of a band's success in music is their ability to inspire people to play music who wouldn't otherwise. And hundreds, probably thousands, have cited Metallica as that inspiration.