CUERNO DE TORO person to whom one is unfaithful. Its origin is uncertain, but it would originate in the last to know is the affected one and that the bull is the only one that cannot see its own horns. I have the theory that the origin is Viking, whose warriors were maritime and took months to travel the Baltic and other distant seas and used bull horns as part of their clothing. It is possible and probable that their wives had forbidden love affairs in the meantime and were considered cuckolds.