People responsible for some of the greatest/epic riffs in my book would be
If you're going to say Keith Richards or Jimmy Page or even Duane Allman, you have to list all of the delta blues musicians (Robert Johnson, Son House, Muddy Waters, Elmore James, etc.) they "borrowed" half of their most famous riffs from.
And most of the others derived from them, in some form or another. I love Slash and Izzy, but to me they derived from that family, even if they are the tops in it. So, hmm... I guess I'll have to think on. Maybe I'll pick later.