Umibōzu (海坊主 "Sea monk") is a spirit in Japanese folklore. He is said to live in the ocean and capsize the ship of anyone who dares to speak to him.
The name of this spirit, which combines the character of "sea", with the character of "Buddhist monk" is possibly related to the fact that the Umibōzu is said to have a large, round head, similar to the shaved heads of Buddhist monks.
Alternatively, they are huge Yōkai that appear to castaways and fishermen. Believed to be the spirits of drowned priests, they display their shaved heads and usually appear to be praying.
They are said to have a gray color, a torso formed by clouds and serpentine limbs. According to one story, if they enrage them, they ask the crews to provide a barrel which they proceed to fill with seawater to drown them.
To avoid this disastrous fate, it is necessary to give them a bottomless barrel.
This tale is probably related to another Japanese tradition, which says that the souls of people who have no one to care for their graves take refuge in the sea.
Umi bozu is a well-known yōkai, who is also recognized in modern Japanese culture.