A vampire who has fallen completely to the Beast is referred to as a Draugr.
The change from life to undeath affects more than a person's body. It changes the soul. A Kindred shares his human consciousness with a force completely opposite to humanity; a thing devoid of reason, conscience or any emotions except hunger and rage. Kindred call it the Beast. Strix call it a gift. Other things that stalk the night and feed on stolen life may experience similar urges and drives, but none so inchoate and instinctual as the Beast within a Kindred.
The Beast is responsible for many of the debased urges kindred feel on a nightly basis. In times of extreme duress the Beast can overwhelm a vampire and force him into a state of pure animalistic drive out of rage, fear, or hunger. Vampires speak of three "heads" of the Beast: The Beast-As-Destroyer, which seeks to rend and smash its enemies, the Beast-As-Tempter, which incites the want for immediate gratification and thoughtless action and the Beast-As-Alpha, which constantly competes with others to assure its dominance.
But the Beast is not a mere mindless force. It has an instinctual drive of its own, recognizing other Beasts like a dog recognizes other dogs by sensing the Taint of the Predator, the unmistakable imprint of a similar force within a being. Their own Predatory Aura constantly tests these other Beasts for dominance, cowing them into submission if necessary or submitting when confronted by a stronger vampire. This friction between vampires is one of the defining forces within the Danse Macabre.