I'll go Tony Alva for the 70s
In the 80s I feel it was constrained by the skating terrain, everyone was skating the same ramps, so I'd have to say McGill for coming up with the Mctwist, and Hosoi for going the highest. Street was inventive but it didn't involve crazy big tricks.
It was the 90s with the people already mentioned like Way, Cardiel, Burnquist and the street guys, who were building bigger ramps, and skating bigger rails and gaps, that the gnar thing became, er, big.