Led Zeppelin certainly inspired heavy metal, but were not a metal band themselves. What they did was light years beyond 'mere' heavy metal. Probably the purest and most innovative rock and roll band ever.
Slight deviation... while I love Led Zeppelin, their "innovation" was really repackaging old blues music into a heavier version. It was great, and did take skill to do so, but I'm not sure I'd call them super innovative for it. I also would have preferred that they gave credit to those blues musicians in advance instead of under duress.