Professor Marcus, identified in the original Japanese version of the series as Hideki Tobishima, is the head of the Akane Island air base around which much of Groizer X takes place. A retired military pilot and a veteran of the Second World War, he brings decades of aviation and combat experience to his role as the senior figure of the Tobishima pilot team. When an unidentified flying object crashes near the island, he and the young aerobatics pilot Joe Kaisaka are the first to investigate the wreckage, where they discover a wounded alien woman named Rita. From that moment, the professor's airfield becomes the staging ground for Earth's defense against the invading Gailar Empire, and he takes on the task of organizing and commanding the ground operations that support Joe and Rita's sorties in the transforming combat craft Groizer X.

Personality-wise, Professor Marcus is a stern and commanding presence. He is described as rigid, austere, and quick to anger, with a temper that occasionally flares up at members of his team, particularly when discipline breaks down or careless mistakes are made. Beneath this gruff exterior, however, he is deeply caring and compassionate. The villagers of Akane hold him in high regard and frequently turn to him for guidance and advice, and within the base he functions as a steady, reassuring authority figure. His strictness is balanced by genuine warmth, and he is shown to be forgiving and understanding even when his patience is tested.

His principal motivation is protecting the people around him and the planet from the Gailar Empire's campaign of conquest. As a former soldier, he understands the cost of war and the importance of strategy, and he devotes himself fully to the defense effort. He works closely with the Japanese military authorities once the base is placed under their oversight, coordinating intelligence, reconnaissance, and defensive measures, while relying on Joe, Rita, and the support crew to take the fight into the air.

The professor's most significant relationships are with the two central pilots. Joe is an orphan who was adopted by the professor as a young boy, and the two share a father-son bond despite Joe's headstrong and sometimes difficult temperament. Professor Marcus is proud of Joe's loyalty and skill even when the two clash. For Rita, he becomes a second father figure, especially because her own father, the scientist Dr. Yan, remains captive and forced to work for the enemy. The professor shelters her, helps her adjust to life on Earth, and offers the stability she lacks while she wrestles with the painful duty of fighting against her own people. His relationship with Baku, an old war comrade who served in the same squadron, is another lasting bond, and he presides over the base's motley crew of mechanics, apprentices, and young recruits such as Sabu, whom he disciplines but ultimately supports.

Across the series, the professor evolves from a peacetime airfield administrator into a wartime commander. As the invasion intensifies and personal losses accumulate, including the deaths of close comrades, his resolve and his grief grow together, and he becomes the emotional anchor of the Akane base. His development is marked by his deepening attachment to Rita and his willingness to sacrifice comfort and safety for the sake of the mission.

Although Professor Marcus never pilots the giant robot and possesses no superhuman abilities, his notable strengths lie in his military experience, tactical judgment, and leadership. He plans the defense of the base, directs operations on the ground, and provides the strategic framework within which Joe and Rita operate. His authority, practical knowledge, and moral clarity make him an indispensable figure in the fight against the Gailar Empire, and his role as a mentor and father figure is central to the emotional core of the story.