Suguru Kinniku, known as Kinnikuman, is the prince and later the 58th king of Planet Kinniku, the home of a powerful race of beings known as Choujin. His life took an unusual turn at birth when his parents, Mayumi and Sayuri Kinniku, accidentally abandoned him on Earth during a family vacation, mistaking the infant for a pig. Growing up alone and in poverty, he constructed a simple one-room house and struggled academically, eventually working a series of odd jobs. In his early adulthood, he was considered a clumsy and ineffective would-be superhero, often causing more collateral damage than the monsters he attempted to fight, which led to him being ridiculed by the very people he tried to protect. His early powers involved eating garlic to grow to a height of 30 meters and using attacks like the Kinniku Flash or Kinniku Beam, though these were often more destructive than heroic.

Personality-wise, Kinnikuman is a study in contradictions. In his daily life, he is childish, arrogant, lazy, and lecherous, often chasing after women and believing himself to be far more popular and handsome than he actually is. He is prone to complaining, pouting when he does not get his way, and even refusing to fight unless he receives some personal reward or incentive. This behavior is compounded by a gluttonous love for gyudon, a Japanese beef bowl dish, which he will go to great lengths to obtain. However, beneath this immature and comical exterior lies a profoundly noble heart. In moments of crisis, especially when his friends are in danger or when facing a particularly dishonorable opponent, his superficial cowardice gives way to immense courage and a fierce sense of justice. It is in these desperate situations that he unlocks his true potential, demonstrating a heroic will that surpasses even the greatest of the Justice Choujin.

His primary motivation evolves over the course of his story. Initially, he seeks fame and recognition, wanting to become a celebrated superhero like Ultraman. However, after his heritage is revealed and he is challenged to reclaim his birthright, his goals shift toward proving his worth as a true hero and a worthy heir to the Kinniku throne. This journey is driven less by ambition for power and more by a deep-seated need for belonging and a growing sense of responsibility for his friends and for the innocent. His defining trait is the Burning Inner Strength, a miraculous ability that allows him to access a reservoir of power in the face of overwhelming odds, enabling seemingly impossible comebacks in his matches.

Kinnikuman’s role is that of the central protagonist and a uniting force among the Justice Choujin. He begins as a pariah but gradually becomes a symbol of hope and a leader, though he rarely acts like a traditional commander. His key relationships are instrumental to his development. His best friend and most trusted ally is the American Choujin Terryman, who started as an arrogant rival but became his inseparable tag-team partner, forming the famous team The Machineguns. Another crucial relationship is with his wife, Bibimba, an assassin initially sent to kill him. Her persistent and unwavering affection eventually transforms his annoyance into genuine love, and they marry, later having a son named Mantaro. He also forms deep bonds with former enemies like the British knight Robin Mask and the cyborg Warsman, who grow from bitter rivals into respected comrades and allies.

Throughout his story, Kinnikuman undergoes significant development. He evolves from a buffoonish and unreliable underdog into a seasoned and respected champion, winning the Chojin Olympics and defeating countless world-threatening evils such as the Seven Devil Choujin. In the later sequel series, Kinnikuman Nisei, he is depicted as an aged and physically diminished king. Having lost most of his muscular physique to age and accumulated injuries, he now has a large stomach and noodly arms. As a father, he made the conscious decision to have all his heroic records annulled to give his son Mantaro a normal childhood, preferring to be seen as a simple, bumbling dad rather than a legendary hero. Despite his physical decline, his tactical knowledge of wrestling and his commitment to justice remain, and he takes on a mentor role, offering guidance to his son and the next generation of heroes from behind the scenes.

In terms of abilities, Kinnikuman's arsenal is vast. His signature and most iconic finishing move is the Kinniku Buster, a devastating technique where he hoists an opponent upside down onto his shoulders before leaping into the air and driving them neck and spine first into the canvas. Other powerful moves include the Kinniku Driver, a modified tombstone piledriver, and the Muscle Spark, a complex and devastating combination hold. As a tag team wrestler, he performs combination moves with his partners, such as the Muscle Docking with Terryman and the Cross Bomber with Robin Mask. In his old age, he can no longer safely perform his high-impact finishers like the Kinniku Buster, forcing him to rely more on grappling, submission holds, and his unmatched experience to prevail in a fight.