The best dunker I've ever seen in person was a kid named Gerry Wright who played at both USC and Iowa, nickname was Sir Jamalot.
Huge hands, lefty. My senior year of HS we played a game at San Jose State where the next game was USC and SJSU. Got to meet Stan Morrison and got to shake hands with Wright whose hands just engulfed mine.
There were rules against dunking in warmups but he was early enough the refs looked the other way as he threw a few down. in dunk contests he could do a legit 360 with 2 balls and dunk both, he called it a 720. He could do a cartwheel dunk where the hand touching the floor had the ball in it, and he could allegedly do a FT line dunk although I never saw him do that one.
Unfortunately that was really all he was good at