THE ARTFULLY RUMPLED uniform sported by downtown creatives—and those who want to look like them—owes a great deal to Steven Alan. But the Manhattan-based retailer and designer, who also owns a showroom that handles worldwide sales for newer labels, is as unassuming as one of his slim-fitting, no-tuck-necessary shirts. When he works the floor of his popular sample sale, he goes completely unrecognized—just another shop guy folding marked-down sweaters.

A native New Yorker, Mr. Alan, 46, opened his first boutique in downtown...