...dance, country, folk, metal and some other things.

If you ask me, rock as a *sound* rather than an ultimately pointless umbrella-term that can include anything from Dylan to Can to brit-pop, it was defined in the early 60's by bands like Rolling Stones, Animals, EARLY Kinks, the Who, Pretty Things and about a 1000 of obscure garage-bands; Namely a "white" take on 50's/early 60's R&B, rock'n'roll, blues etc.-tough, hard (hard-rock is really an oxymoron IMO even if the pomposity and bombasm of much music in that genre isn't really "true" rock to me), asskicking stuff.
Artists like Hendrix, Cream, Blue Cheer, Zeppelin, Stooges, MC5 etc. continued and developed it later as well as AC/DC and Motörhead in the 70's and bands that continued in that vein later.

IMO, few of the hyped modern bands make "pure" rock IMO outside of obvious choices like Black Keys, White Stripes etc...