He has known, and apparently had a close relationship with, the witch Flora for at least several hundred years and was also one of the previous owners of Berserker Armor. Flora and the Skull Knight both acknowledge Void's existence, but the exact history of their relationship remains ambiguous.
He is a large skeleton figure with yellow eyes and spikes coming from his shoulders and head. He also wears a gray cape which covers his shoulders.
The Skull Knight is an enigmatic figure who fights against evil. He is shown to care for others, as he has saved Guts several times. He is also shown to have a close relationship with Flora the witch as he met her often and Flora always looked at the Berserk Armour with tenderness. He has also rescued Rickert from the apostles and Luca from the egg shaped apostle.
The Skull Knight first appears to warn Guts about the Band of the Hawk's impending demise following his leave. He called Guts a "Struggler" against fate before disappearing elsewhere.
Shortly before the Eclipse, the Skull Knight appears again to protect Rickert from the Count and Rosine, who both leave upon seeing his presence.
The Skull Knight first battles with Nosferatu Zodd, who guards the outside of the gate in order to fight against his adversary again. After defeating Zodd, he rushes into the ceremony, smashing through the portal and interrupting the ceremony in the process. He immediately attempts to attack Void, with little success, as Void projects an alternate dimension to send the Knight's incoming sword back out in a mirror effect. The Skull Knight then blocks the attack with his shield and exchanges glances with Void for a moment before going to save Guts and Casca from further harm. The Skull Knight then makes short work of many Apostles in mere seconds and dodges Femto's Apostle implosion attack with ease before heading straight out of the window he came in. As Rickert heals Guts and Casca with the elf dust that Puck gave him, Zodd allows the Skull Knight to take Guts and Casca, as a mark of respect for being defeated in battle. The Skull Knight then transports the three humans to Godo's cottage, and four days later, shows Guts the demonic world he will be living in, allowing him to borrow his sword to defeat the ghosts attacking him. He finally explains Casca's early childbirth and the characteristics of the Demon Child before leaving.
The Skull Knight later appears in Misty Valley to swallow Rosine's Behelit.
He appears later near St. Albion to warn Guts of the Incarnation Ceremony and tell him of the God Hand's and abilities, stating that he can either choose to kill Griffith or save Casca, but cannot do both. At St. Albion, he chases down the Egg-Shaped Apostle and rescues Luca from its lair.
The Skull Knight enters the Qliphoth to confront Slan and to assist Guts. Similarly to the Eclipse, he easily takes down the Ogres attacking him, distracting Slan long enough for Guts to attack her with his arm cannon and later with the Dragon Slayer. When the Qliphoth collapses, the Skull Knight uses his Sword of Resonance to escape with Guts in tow.
The Skull Knight confronts Flora about the serious consequences of giving Guts the Berserker Armor, hearing Flora's assent that it must be so. As Griffith's Apostle army comes to burn down Flora's home, the Skull Knight engages the Apostles and Zodd, after telling Flora that if she dies it should be peaceful, again before witnessing Guts' first use of the Berserker Armor against a transformed Grunbeld. When questioned by Zodd, who recognize the armor after look at it with surprise and fear, on why would he give Guts the armor, but the Skull Knight give no answer and the both stop their fighting to watch Guts and Grunbeld.
The Skull Knight appears in front of Guts' party at the beach, warning him that what he wants may not be what Casca wants.
Skull Knight appears with his Sword of Resonance and slashes at Femto to stop the transformed Ganishka. Femto manipulates the slash to hit Ganishka instead, triggering a light that covers the world and causes the astral realm to collide with the physical realm, allowing many astral beasts to enter the physical realm and Griffith's castle to appear underneath the deceased Ganishka's body.