Vikings never actually wore horned helmets — it was invented by a 19th-century costume designer

Not a single horned helmet has been found in any Viking archaeological site. The horned helmet image was largely popularised by costume designer Carl Emil Doepler for an 1876 production of Wagner's opera Der Ring des Nibelungen. Prior to that, a 1736 painting by Swedish artist Martin van Meytens showed a Scandinavian warrior with a horned helmet, spreading the image. Real Viking helmets, like the only intact example found (the Gjermundbu helmet from 970 CE), are simple rounded iron caps, some with a nose guard.