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 one of Alucard's many familiars in the Hellsing series.

Description
Its form varies, but it usually appears as a large dog with shaggy black fur, multiple red eyes, and a large, fang filled mouth. It typically emerges from either one of his arms, almost serving as some sort of extension for his selected limb. Baskerville appears to be one of Alucard's favorite familiars, since he tends to use it against opponents he considers challenging.

In Hellsing
It wasn't uncommon for Alucard to take on a dog-like form, the canine appearing shaggy and black with multiple eyes of crimson color. It is unknown if this is purely Alucard's shape shifting ability in action or if the vampire has taken on the dog's visage to inconspicuously navigate throughout humanity. However, the dog has multiple red eyes which undermine the efforts of the latter possibility, so it is likely the former.

In Hellsing Ultimate
Baskerville is first seen in Hellsing Ultimate as the Valentine brothers assail the Hellsing Manor. While Jan Valentine causes havoc uptop, Luke Valentine heads below to face off with Alucard. It isn't until Luke's speed and banter pique the Vampire's interest does he actually summon the dog first. The fight is quickly concluded after he does so, with Luke being devoured by Baskerville.

Later, Baskerville appears as Alucard faces off with a vampirized Walter. Despite the previously seen ferocity and strength of the creature, it isn't able to contend with Walter's Monofilament Wires. Upon dying, Luke Valentine was released from its bowels.

Trivia

 * The name "Baskerville" is a reference to the Sir Arthur Conan Doyle novel, "The Hound of the Baskervilles". Its name was revealed in Volume 9, when Alucard summoned it against Walter.
 * 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 Valentine's.
 * In the anime, after Alucard is killed by Incognito, he returns from hell in the form of Baskerville.
 * In Hellsing Ultimate, its eye makes out the shape of the word "shit" as it devours Luke Valentine.
 * In the English Dub of Hellsing Ultimate Jonathan Klien was originally going to name Alucard's familiar Cerberus due to the fact the Dog had two heads with Alucard's head as the third. In Greek Mythology, Cerberus was a Hellhound who guarded the gates of Hell for Hades.