beast of darkness (berserk)

In Berserk, the Beast of Darkness, also known as the Hellhound, is Guts' inner beast, the manifestation of all the hatred and evil that has dwelled within his soul since the Eclipse. It takes the form of a great black houndlike wolf with sinister-looking flaming red eyes. It taunts him, questioning the morality of his quest for revenge against Griffith and urging him to commit ever-greater atrocities, with the ultimate goal of turning him into a monster.

As the Black Swordsman, Guts and the Beast worked in concert, and the path of revenge and bloodshed that Guts walked after the Eclipse allowed the Beast to grow in power. When Guts found Casca again and started thinking about things other than revenge, the Beast began to work against him, and has begun attempting to convince him to give into his dark desires and kill her so that he can get back to his vendetta against Griffith. The Berserker Armor, though it increases Guts' fighting power against the demonic Apostles that he fights, gives power to the Beast every time he goes into Berserker mode, and only with the help of his newfound friends has Guts managed to keep the Beast at bay.