Griselbrand

Griselbrand was one of the demonic masters of Liliana Vess. He lived on Innistrad. He fought the archangel Avacyn and the two of them clashed, with Avacyn gaining the upper hand. He was imprisoned in the Helvault, an artifact of immense power, made of pure silver, but Griselbrand, in a last-ditch effort to obtain revenge, threw his spear at Avacyn, taking her with him.

Liliana Vess visited Innistrad in the hopes of destroying Griselbrand, with whom she had made a demonic pact that would result in her soul's enslavement. To this end, she opened the Helvault by forcing an ultimatum on Thalia, its guardian. Immediately after his release, Griselbrand used his freedom as an opportunity to escape Avacyn. However, Liliana tracked Griselbrand down, slaughtering both angels and demons alike, and finally cornered him. Desperate, Griselbrand bribed Liliana with promises of power, but she saw through his lies and used the Chain Veil to kill him permanently.

Trivia

 * In "The Saint, the Geist, and the Angel", the narrator states that Innistrad demons are made of pure black mana, which allows them to regenerate after death. However, Griselbrand's death appears to have been permanent. It is unclear if the Chain Veil's power deprives demons of their immortality or if this was just a writing inconsistency.