Namahage

1968 anime:
Daisuke Azuma, an intelligent but not polite young man, became a Namahage after wearing a mask of a Namahage kept at a shrine and played pranks with it, but accidentally killed an old man called Roppei by shocking him. Horrified, he took the mask off, but found that his face now resembled a Namahage. However, Roppei, thought to be dead , was not only alive, but actually a real Namahage.

2007 anime:
He is the 13th of the chosen 47 Youkai Warriors of Japan and the representative of Akita.

(Source: GeGeGe no Kitarou Wiki)