His broad shoulders and massive wingspan, tapering to a slim waist and short legs make him perfectly streamlined for the pool.
He proved it in Beijing with a record-breaking week-long medal binge that eclipsed Mark Spitz's achievement 36 years earlier in Munich.
Despite his gargantuan workload, Phelps always did just enough. His seventh gold, in the 100m butterfly, saw him pip Milorad Cavic by the narrowest margin. The Serbian touched the wall first, but Phelps did so more forcefully, triggering a victory by just 0.01 seconds.
The American's crowning glory came in the 4x100m medley relay, in which he set the fastest butterfly split of all time in the third leg, and Jason Lezak held on to secure Phelps a permanent place in Olympic legend.
It may have lacked the explosiveness of Usain Bolt, the artistry of Nadia Comaneci or the significance of Jesse Owens, but for sustained brilliance, Phelps's achievement surpassed them all.