When one has newly embarked on building an empire-within-an-empire, as Hedi Slimane did last year at Celine, it is helpful to have already had some experience with creating fragrances.

Directing a perfumer in the creation of a perfume is unlike directing anything else in the world. But Slimane had prepped for this role, to a great extent without really consciously preparing for it at all.

He...