Baskerville

Baskerville（バスカヴィル, Basukaviru), also known as the Black Dog (ブラック・ドッグ, Burakku Doggu), is a hellhound that Alucard controls.

Baskerville is one of Alucards favorite familliars considering the fact that he uses it alot.

The name Baskerville is a reference to Sir Arthur Doyle novel "Hound of the Baskervilles" as Walter simply calls it Baskerville.

It seems to be able to absorb powers for itself as in the case with Luke Valentine, as Alucard states that it wasn't a complete waste to feed him to his dog, after observing it's speed and movements similar to Valentines.

If Baskerville really dies is unclear, but it's seems so as Luke Valentine appears after it's cut in half by Walter. In the anime after Alucard is killed by Incognito, he returns from hell in the form of Baskerville dog.