Withengar

Withengar is a powerful demon from the plane of Innistrad. He is infamous for slaying Saint Traft.

The saint, the geist, and the angel
Prior to the events of Innistrad block, the Skirsdag cultists led a monster slayer named Saint Traft into a trap. They blinded him and switched the sword on his hand for Elbrus, the Binding Blade, the Binding Blade. Traft slew the cultists with this weapon, inadvertently summoning Withengar in the process, a dreadful demon whose essence was bound in the bone sword. Withengar ended the life of Traft while laughing.

His victory did not last long, since Innistrad's angels vengefully attacked him and destroyed his physical body. However, Withengar did not die, but reverted to pure black mana. Without being attached to the sword or any restrictive spell, it would only a matter of time for the demon to reincarnate and feast yet again upon Damnation of the plane.

Dark Ascension
Withengar was reincarnated during the events of Dark Ascension, which were caused by the absence of Avacyn.

In-game references
Represented in:
 * Withengar Unbound

Trivia

 * The artist Eric Deschamps originally intended for Elbrus, the Binding Blade to be Withengar's severed finger and planned to draw Withengar with a missing finger. On the final card art, Withengar has all of his fingers.
 * Withengar Unbound is the only legendary double-faced card in the Innistrad block. It was the only legendary double-faced card in the game until Magic Origins released double-faced planeswalkers.
 * Withengar is believed to be the most powerful and dangerous demon in the known Multiverse. However, it would be hard to compare his powers directly to those of demons from other planes, such as Rakdos or Ob-Nixilis.