The character referred to as the Principal of Wammy's House in Death Note is Roger Ruvie. He is the elderly manager of Wammy's House in Winchester, England, the orphanage established by Watari to identify and train exceptionally gifted children as potential successors to the detective L. When Watari is not present, Roger oversees the daily operation of the facility, and he continues in this administrative role after Watari's death.

Roger is a close friend and longtime associate of Watari, and he assumes leadership of the orphanage from him. He is an elderly man with a balding head of gray hair, brown eyes, and a slight build, and he is usually seen wearing small round glasses and a brown coat. He is described as grumpy and studious. Despite his position as the head of an orphanage, he openly dislikes children and prefers to spend his time with his collection of books about insects.

In terms of personality, Roger is serious, reserved, and quietly dedicated to his duties. He is organized and able to remain calm under pressure, working behind the scenes rather than seeking attention. His aversion to children makes his interactions with the young residents of Wammy's House somewhat distant and awkward, yet he still carries out his responsibilities toward them out of a strong sense of duty.

Roger's motivations are rooted in loyalty to Watari and respect for the legacy that Watari and L built. After learning of the deaths of both L and Watari, he is genuinely saddened, and he takes up the role of the new Watari to ensure that the work of catching Kira continues. In this capacity, he supports Near, the successor who becomes the third L, providing logistical support, acting as a liaison, and serving as a trusted advisor in the investigation. He also proposes that Near and Mello work together to pursue Kira, though Mello refuses on the grounds that their personalities are too different.

Roger's key relationships are defined by his connection to Wammy's House and its generation of prodigies. Watari is his closest ally, having entrusted him with the orphanage. Near is the successor he informs of his selection and later serves as his Watari, working alongside him in the final stage of the investigation. Mello is another candidate whom Roger watched leave the house to follow his own path. L, as the most famous product of Wammy's House, is someone whose death Roger mourns deeply.

Through the course of the story, Roger develops from a background administrator into a crucial supporting figure in the hunt for Kira. He demonstrates adaptability by stepping into Watari's position and dedicating himself to the next generation of detectives. His notable abilities include the administrative skill to run Wammy's House, the organizational talent to support a complex international investigation, and the composure to work quietly in the background while younger successors take the lead.