Aatxe is a spirit in the folk mythology

Basque mythology

The mythology of the ancient Basques largely did not survive the, albeit late, arrival of Christianity in the Basque Country between the 4th and 12th century AD...

 of the Basque people

Basque people

The Basques as an ethnic group, primarily inhabit an area traditionally known as the Basque Country , a region that is located around the western end of the Pyrenees on the coast of the Bay of Biscay and straddles parts of north-central Spain and south-western France.The Basques are known in the...

. His name is literally translated as "Young Bull", and he is sometimes known as Etsai. He is a cave

Cave

A cave or cavern is a natural underground space large enough for a human to enter. The term applies to natural cavities some part of which is in total darkness. The word cave also includes smaller spaces like rock shelters, sea caves, and grottos.Speleology is the science of exploration and study...

-dwelling spirit who adopts the form of a young red bull, but being a shapeshifter

ShapeShifter

ShapeShifter is an Application Enhancer plugin for Mac OS X developed by Unsanity that allows the user to make system-wide modifications to the appearance of the operating system's graphical interface by applying GUI skins through “injection” into running code and without modifying system files,...

, sometimes takes the shape of a man. At night, more so in stormy weather, he arises from the hollow which is his lair. He attacks criminals and other malevolent people. He also protects people by making them stay home when danger is near.

He is theorized to be a representation of the goddess Mari

Mari (goddess)

Mari, Mari Urraca, Anbotoko Mari and the possibly distinct Murumendiko Dama was a goddess — a lamia — of the Basques. She was married to the god Sugaar...

, or may be an enforcer of her will, punishing people who cheat her. Another name for him is Aatxegorri which means 'young red bull'.