My eyes pass swiftly over most fashion ads, which can be counted on to feature pretty models looking sexy while posing with fill-in-the-blank lipstick, clothes or jewelry.

But the new Louis Vuitton ad featuring Muhammad Ali made me pause. The three-year-old in the photo – shot last month by Annie Leibovitz – holds a feet-apart-chest-out stance that seems to say the same sort of thing his 70-year-old grandfather once brashly blurted: "I'm puuritty. I'm the grrreatest."

I...