Martin Hennes is the older brother of Sophia Hennes, known as Sophie, in the anime Garo: Vanishing Line. He is a skilled computer programmer and system engineer who, together with Sophie, lived in a slum without relying on relatives. He developed a technology that could access virtual reality solely through a retinal scan, bypassing the need for surgery or chip implants, and published a paper on his invention, though most companies did not recognize its value. Martin's disappearance occurred after he began investigating the mysterious phrase El Dorado, which became the only clue left for Sophie. His absence serves as the primary motivation for Sophie's journey, as she spends years searching for him. Martin is characterized by his intelligence, resourcefulness, and care for his sister, as he took responsibility for their livelihood. Beyond his technical abilities, little is known about his personality, as he is missing for the majority of the story and appears only through Sophie's memories and the lingering impact of his research. His role is crucial as a catalyst, setting the plot in motion and connecting the protagonists to the secrets of El Dorado.