Augustus, often called Gus by those close to him, is a specter and a central supporting character. He is the foster grandfather of the protagonist, William, and one of three undead beings who raise the human child in the City of the Dead. In life, Augustus was a human known as the Wandering Sage, a title reflecting his vast knowledge and skill in magic. After his death, he made a contract with the goddess of undeath, Stagnate, to return as an undead, becoming a specter with white hair and blue eyes.

In terms of personality, Augustus presents himself as harsh, rude, and haughty, particularly towards William. This gruff exterior masks a deep-seated care for his family and friends. His pride as a powerful sorcerer often overwhelms his sense of humility, leading him to act like a cantankerous old man. Despite his constant rude remarks to William, he never harbors any genuine hatred for him and eventually comes to see the boy as the grandson he never had. His primary driving motivation is the pursuit of knowledge, a trait that defined him in life as the Wandering Sage and continues to do so in his undead state.

Within the story, Augustus plays a pivotal role as one of William's three adoptive guardians in the City of the Dead. He is responsible for teaching William magic and unlocking his affinity for the mystical arts. After the defeat of Stagnate, the goddess Gracefeel offered Augustus and his companions an extension to their afterlife contract. While the other two chose to have their life forces recycled into the normal cycle of death and rebirth, Augustus alone accepted the extension, becoming something akin to a herald of Gracefeel to continue his duty protecting the seal of the High King. He is also the one who devised the strategy for the trial he and his companions put William through to test his worth.

Augustus has profound relationships with his fellow guardians. Alongside Mary, a mummy, and Blood, a skeleton, he forms an unconventional family unit dedicated to raising William. These three were once human adventurers together, and their bond from life carries into their undeath. Of the three, Augustus shares a particularly unique dynamic with William, acting as a strict and demanding magical tutor who gradually reveals his genuine affection for the boy. His relationship with the divine is also key; his contract shifts from the goddess Stagnate to the god of death, Gracefeel, fundamentally changing his purpose from a standard undead to a divine guardian.

Augustus is a static character who provides wisdom and challenge rather than undergoing a significant personal transformation himself. His primary development is the evolution of his relationship with William, as he moves from a mysterious and frightening ghost to a respected grandfather figure. He also makes a critical choice to accept Gracefeel's contract, solidifying his resolve to continue protecting the seal he and his party were originally bound to defend, ensuring his continued existence in the world.

His most notable ability is his mastery of the Words of Creation, an ancient and powerful form of magic. He is skilled enough to perform multicast spells in rapid succession, unleashing a barrage of magic against his enemies with ease. His vast accumulated knowledge, a hallmark of his time as the Wandering Sage, makes him an exceptional tactician, capable of devising complex strategies even if they have unforeseen flaws.