Bucephalus
Alexander the Great's favorite horse, from Greek Boukephalos, literally "Ox-head," from bous "ox" (see cow, n.) + kephale "head" (see cephalo-).
Men called [him] Bucephalus ... of the marke or brand of a buls head, which was imprinted vpon his shoulder. [Pliny, I.220, tr. Holland, 1601]