dullahan
http://en.wikipedia.org/wiki/Dullahan
From Wikipedia, the free encyclopedia:
"The Irish dullahan (also Gan Ceann, meaning "without a head" in Irish) is a type of unseelie fairie. It is headless, usually seen riding a black horse and carrying his or her head under one arm.
The dullahan is portrayed in fantasy fiction and video games as a beheaded knight who carries his severed head under one arm while viciously attacking interlopers in the place that is haunted by the dullahan. They also have some magic in their bodies, giving them magical swords or the ability to breathe fire from the severed head. Alternatively, the dullahan may be an animated suit of armor, the best example of which is Dullahan, an optional final boss character in the Golden Sun games, or the Durahan species of monster in Monster Rancher."