At their peak:
Baseball: Andrew Jones (could do it all)
Hockey: Lemieux
Football: Gronk (only truly unstoppable player)
BB: Jordan (though Magic most fun to watch)
Soccer: Renaldo
Tennis: Nadal
Golf: Tiger
Summer Olympics: Edwin Moses
Winter: Eric Heiden
Motocross: Carmeichal
MotoGP: Rossi
F1: Schumacher (never saw Senna)
Nascar: Cale Yarborough
Horse: Skip Away
Chess: Fischer (read his games)
Bowling: Weber
Boxing: Sugar Ray
Baseball: Andrew Jones (could do it all)
Hockey: Lemieux
Football: Gronk (only truly unstoppable player)
BB: Jordan (though Magic most fun to watch)
Soccer: Renaldo
Tennis: Nadal
Golf: Tiger
Summer Olympics: Edwin Moses
Winter: Eric Heiden
Motocross: Carmeichal
MotoGP: Rossi
F1: Schumacher (never saw Senna)
Nascar: Cale Yarborough
Horse: Skip Away
Chess: Fischer (read his games)
Bowling: Weber
Boxing: Sugar Ray