remember this guy? isnt he the original guy that sold steroids as legal sups and then got busted?

Conte was a major player, but I think it might have to go to Pat Arnold (he was Conte's supplier) -

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He was always the guy most went to to formulate this type of stuff, and he always had a few fingers in the prohormone pie going way back.
A little bit after the passage of DSHEA, tons of guys were having dreams about bringing harder prohormones and orphan steroids to the market as supplements. I think Arnold, Duchaine, and Stan Antosh might have been the first with OSMO prohormones, then after that home run race between Sosa, McGwire, etc.... a ton of guys entered the market.
It's an interesting question, there's perhaps 3 - 4 different periods in prohormone history.