I just happened to see this picture of Katie Ledecky today --
-- and it struck me whom she resembles: Olga Korbut.
Each woman is among the greatest ever in her sport (and Ledecky is far from through).
But while they resemble each other facially, and both have huge smiles, they have completely different builds. Korbut was a pixie-like 4'11" and 84 pounds at her peak, as befits a champion gymnast, whereas Ledecky is listed at six feet on the Stanford roster and looks as if she weighs roughly 160.
(It would have been so much cooler if her Stanford bio had merely said "Katie is a passable distance freestyler" rather than exhaustively listing her every last accolade; it's not as if anyone who'd ever go to that website might possibly be unaware of her accomplishments.)
Ledecky, according to Wikipedia, is a quarter Czech, a quarter Jewish, and half Irish. Korbut was born in western Belarus, near the Polish and Lithuanian borders. So their ethnicities are not identical. But from the neck up, they look as if they could have been sisters.