Rowdy is a dog with unusual markings that he wasn’t born with, but developed over time. It’s the result of vitiligo, a condition that affects the pigmentation of skin.
Because of his look, and even more because of his friendly attitude and popularity, Rowdy has become the mascot of the the American Vitiligo Foundation. -via Tastefully Offensive
PS: Rowdy is also the subject of a recent reddit Photoshop battle.