The Dullahan (also Durahan, Gan Ceann) is a type of undead legendary creature. It is headless, usually seen riding a headless black horse and carrying his head under one arm. The myth may have inspired The Legend of Sleepy Hollow.
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. In the Castlevania series, the Dullahan is headless, carrying a demonic shield inscribed with a face which acts as its head.
Anna's Irish folklore (http://members.tripod.com/~pg4anna/Irish_folklore.htm)