Helmets with horns have become an icon that is closely associated with Vikings, but there is no real evidence, either in historical art or existing physical artifacts, to support the idea that these people actually wore helmets that were adorned with things like horns or wings. Though Greek and Roman texts from the ancient world suggest that some invaders did have some unusual tastes in headwear, including animal heads, it appears that the idea of a Viking wearing a helmet with horns or other embellishment such as wings is a much more recent invention dating back to the 17th-19th century C.E.
The romanticized version of a scary Viking helmet is likely derived from the above-mentioned ancient Greek and Roman texts, which were written about people who existed before Viking society was really established. Going off of available evidence, it is safe to say that Vikings did sometimes wear some kind of helmet-like head gear made of leather and even wood, but most of the time, they tended to wear nothing on their heads at all. Some higher-ranking Vikings may have worn crude metal helmets made of early metals such as bronze or iron, but this protection wasn't available to everyone, and metalworking technology of the time would have made elaborate embellishment difficult.