Even though there are lots of history paintings with Vikings or Germanic warriors wearing horned helmets it is sure that this is a pure invention. Celtic warriors or some Etruscans may have had helmets with horns or wings. The few depictions in Northern Europe belong to older times, the Bronze Age, and are probably showing helmets for ceremonial purposes.
Illustration by N.C. Wyeth for the Arthur Conan Doyle story "The First Cargo", published in Scribner's Magazine, December 1910.
Germanic warriors with horned or winged helmets were a typical invention of 19th century Romanticism, probably because they look so barbarian and exotic. The creation became popular when costume designers used the idea for the heroes and gods in Wagner’s operas.
Later this pure fantasy-invention became so popular that even Danes of today put on these helmets to look like real Vikings. So it’s at least a nice example how the iconography of history painting influenced reality.
9 hours ago