Cernunnos was a Celtic god, probably of fertility
Cernunnos was depicted with stag's springtime horns, and in fact the "Cer" of his name is likely an old Celtic root for horn.
"Old Hornie" as he was called, was associated strictly with the male aspect of fertility. It is possible that he could have been the male participant in the ancient fertility rituals of spring, the death of the old god and his rebirth as a young one. It is also very possible that his horned representation was the inspiration for that aspect of the devil's appearance.