Probably Jack Adams, mid 1930s Red Wings, ran a five forward PP. Then various coaches in the 1940s - Hap Day, Toronto with Max Bentley, 1950s Montreal- Dick Irvin with Bernie Geoffrion, then Toe Blake with Geoffrion and Bobby Rousseau after Geoffrion retired initially.
Ya thats the one I recall reading about somewhere, attribution given to Jack Adams, who I think may well have borrowed it himself from his previous career as a player so it very likely goes back even further than that... though not in the same way that we think of, recognize PP's today as back in Jacks' day as a player rosters were much smaller, played considerably more minutes, and going way back, you played the whole game. So when penalties assessed, what wouldve been instituted wouldve been "set plays" or in modern parlance, "picks". Usually 2-3 set, rehearsed & practiced moves in deep on the offence on the PP including from the Face-off dots.
Back in the early 80's Eddie Johnston then with the Penguins is credited with first introducing "pick plays" however I dont think so, disagree. Goes way back but was altered with increased roster sizes, flexibility resulting thereof, the #1 line usually on the PP with an addition like Geoffrion playing on the Blue Line or back, like a Rover, shooting off his Cannon from top of the slot or back even further. The Center still acting as QB on the PP. What EJ did, and the most successful PP in all of Penguins history (scoring 99/400 chances = 24.5% success ratio in 81/82), superior to those later employed with guys like Lemieux, Coffey & Jagr, was to employ 3 Centers & 1 Defenceman on the PP, namely Randy Carlyle who acted as QB, with Mike Bullard, Pat Boutette, Paul Gardner & Rick Kehoe (RW). They had 3 "picks" or set plays, a tactic EJ borrowed from basketball, from Coach Tom Heinsohn of the Boston Celtics who Johnston got to know well during his many years in Boston. So not your top line but instead, total specialization, special unit, picks, set plays down low, mid high, top shelf. Bullard with a Cannon, Boutette & Gardner big, tough, nasty with the stickwork down low & mid-high, Kehoe the Sniper, Carlyle the QB.
... and so yes, yes once again C58, if you want genius, innovation, look to & for.... a goalie.