Obviously it's The Who
Obviously as its they who invented the beast. No Hendrix was not the guy who turned up his amp and started playing outrageously loud. It was Townsend and the Who. They invented hard rock along with bands like Blue Cheer.

Floyd is probably the greatest prog rock band of all time however. Zep the 2nd best blues based rock band behind Cream IMHO.

The Who are basicly a hard rock band that ventures into prog. Listen to Live at Leeds and see what I mean. These guys held the record for the loudest band in concert for decades.