Jeffry Fuhrmann is a dunker known inside the sport for the 720, the double-rotation dunk that only a handful of people have landed.
He is also one of the people other dunkers go to when they are trying to learn it. Dylan Haugen has credited a conversation with Fuhrmann as the thing that made the 720 click for him, specifically the cue to go straight up rather than spinning out of the jump. That is a small correction and it is the whole difference: spinning out of the takeoff bleeds the height you need to complete two turns, so the rotation has to come from the shoulders and hips rather than from the run-in.
The 720 is the most technically demanding dunk in the sport. Two full rotations means the rim is out of sight for almost the entire jump and the ball has to be placed by feel at the exact point the second turn finishes. Dunkers who can hit it reliably are counted in single figures worldwide.
He is on the shortlist for the Dunker Survey, the dataset that only accepts jumpers with a verified 40 inch vertical or better.