Mozgus is one of the chief Inquisitors of the Holy See, traveling the world with his group of torturers to root out heretics. Sent to the city of St. Albion, he aims to eliminate a violent cult of heretics. As the main antagonist in the Tower of Conviction, his excessive religious zeal hinders Guts' efforts to save Casca. His symbol is four torture wheels, representing his belief in using torture to cleanse people from evil.
Before the events of the Resurrection Arc, Mozgus was already a zealous Inquisitor working for the Holy See. He recruited a small group of marginalized and disfigured individuals, offering them comfort through readings from the Holy See Doctrine. He assured them that their disfigurements were gifts from God to be worn with pride and trained them in his brutal methods of torture, which rarely left survivors unscathed.
Dispatched to St. Albion to root out heresy on behalf of the Holy See, he requested the Holy Iron Chain Knights as his personal guard. Although a genuine heretical group was active in the mountains around St. Albion, engaging in orgiastic rituals, Mozgus did little to stop them. Many were captured only due to Farnese's intervention. Instead, he focused on crushing rebellions among the poor and starving population of St. Albion, who were rebelling against the tyrannical rule of the Holy See. To Mozgus, defiance against him was defiance against God, whose rule he believed he embodied.
Tall and strong, harsh and demanding with everyone, including himself, Mozgus impressed Farnese by quelling several rebellions with threats of death and torture. He spared only a young mother pleading for food for her starving child. Though he provided food and medical attention for the child, he sentenced the woman to torture, praying tearfully that she would survive "God's test." He used this encounter to teach Farnese about the harshness of God's doctrine.
Upon capturing Casca, mistaken for a witch by both local heretics and priests, Mozgus realized that recent accounts of the Black Swordsman might be related to the mute, amnesiac branded girl. As usual, he tried to extract information through torture. Instead, he inadvertently triggered the appearance of a huge band of demons, drawn by the Tower itself, chosen for the Incarnation Ceremony due to the presence of the Brand. Unfazed, Mozgus retreated to the chapel of the Tower of Rebirth, where an Apostle-Behelit transformed him and his servants into Apostle-spawns with angelic features, hastening the Incarnation Ceremony.
Unaware of what had happened to him, Mozgus believed that his newfound angelic wings, increased stamina, and scaly hide resistant to blows from the Dragonslayer and Guts' arm cannon were gifts from God. Determined to stop the Ceremony and quell public fears, he decided to burn Casca at the stake, forcing Guts to come out of hiding.
After a fierce battle against his mutated servants, Mozgus nearly defeated Guts. However, Guts managed to drive his sword into the only weak spot in Mozgus' hide: a small, weaker plate bearing the Holy See insignia, a representation of the Holy Book Mozgus always carried. Shortly after his death, the Incarnation Ceremony was completed, resulting in Griffith's rebirth and the total destruction of St. Albion.
