A character with a removable head.
In Irish folklore, the Dullahan is a headless rider or 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 anime and videogames, the Dullahan is sometimes portrayed as an animated suit of armor. Examples include Dullahan from Golden Sun, an optional final boss character, or the Durahan species of monster in Monster Farm.