AATXE
European Folklore
A type of Spirit or Devil
This is the name of an evil SPIRIT or devil in the folklore of the Basque people of southwestern France and northwestern Spain. Aatxe, which means Young Bull, is also known as Etsai. This spirit is a shape shifter who most frequently appears in the form of a bull, but may also assume the shape of a human. Aatxe inhabits mountain caves, from which he emerges only on stormy nights to wreak havoc and cause destruction.
Source: Spirits, Fairies, Leprechauns, and Goblins Encyclopedia