Professor Hayao Sato is a supporting character in the 2024 animated film Ultraman: Rising. He is publicly known as a professor and one of the world's foremost experts on kaiju, the giant creatures that periodically threaten Japan. His real identity, however, is that of the previous Ultraman, a silver giant from beyond Earth who once protected the world before passing that responsibility to his son. In his later years he is sometimes known as Ultradad.

His background is defined by duty and sacrifice. He is the father of Ken Sato, a star baseball player who inherits the Ultra powers, and the husband of Emiko Sato, who disappeared some years before the film's events. His long commitment to fighting kaiju and studying them left him little time for family life, which created a lasting rift between him and his son. After sustaining a crippling injury and losing his wife, he retreated into seclusion, living quietly with his research until Ken returns to Japan.

In personality, Sato is reserved, scholarly, and methodical, with a formal academic manner. He carries deep guilt over the cost his family paid for his role as Ultraman and tends to keep emotional distance. Beneath this guarded exterior lies genuine care and a strong desire to make amends. He also shows tenderness and scientific fascination toward the infant kaiju Emi, treating her as both a remarkable subject and a member of the family.

His motivations center on protecting humanity, maintaining a balance between humans and kaiju, and guiding his son to understand the true weight of being Ultraman. He is equally driven by the wish to repair his relationship with Ken and to find some form of redemption for his perceived failures as a husband and father.

In the story, Sato begins as the estranged predecessor who has already passed the Ultra mantle to Ken. He functions as a mentor figure and, at first, a source of tension. When Ken finally reaches out for help while struggling to raise the baby kaiju, Sato heals the creature, names her Emi after his missing wife, and assists in her upbringing. His role expands when he is injured during an attack and placed in a healing tube, only to return later in his original form as Ultradad to save Ken during the climactic confrontation. He joins the final battle and afterwards helps locate the hidden kaiju island.

His key relationships shape the film's emotional arc. With Ken, he shares a strained father-son bond that gradually heals as Ken comes to understand the demands of parenthood and heroism. With Emi, he develops a gentle, grandfather-like attachment, and his decision to name her after Emiko reflects his enduring love and regret. His relationship with Emiko was warm but burdened by his duties, and her disappearance haunts him throughout the story. He also has a connection to the AI assistant Mina, as her creator and as a quiet presence in the Sato household.

His development follows a movement from isolation to participation. He starts as a distant, guilt-ridden recluse and becomes an engaged parent and ally. The turning point comes when Ken, having experienced the struggle of caring for a child, finally understands his father's choices, allowing the two to reconcile. Sato then steps back into battle not to reclaim his former role, but to fight alongside his son, which symbolizes the mending of their relationship and the passing of the torch.

His notable abilities include the powers of an Ultra, such as transforming into a towering armored form, superhuman strength, flight, endurance, and energy-based attacks. Beyond combat, he is a brilliant scientist with deep knowledge of kaiju biology and the history of the Giants of Light. His expertise extends to advanced technology, including healing methods and devices that allow him to treat injuries and support others in their recovery.