Suguru Kinniku, known as Kinnikuman, is prince and eventual king of Planet Kinniku. Accidentally abandoned on Earth as an infant when his parents, Mayumi and Sayuri Kinniku, mistook him for a pig during a vacation, he grew up alone in poverty. He performed odd jobs and initially dreamed of becoming a superhero like Ultraman. His physical strength was undermined by clumsiness and lack of intelligence, leading him to settle as president of the Gyudon Lovers Club.

Considered a worthless chojin in early adulthood, the Earth Defence Force contacted Kinnikuman to fight space kaiju when other heroes were unavailable. He developed his first finishing move, the Kinniku Beam, though his missions often ended comically without combat. His life transformed when Alexandria Meat found him, revealing his royal lineage and recruiting him to reclaim Planet Kinniku from a usurping pig. After losing a judo-boxing-wrestling match to King Tone, the pig fled, allowing Mayumi to reclaim the throne. Kinnikuman chose to stay on Earth, continuing his superhero pursuits.

Kinnikuman exhibits a childish, arrogant, and lazy personality, often complaining when overlooked or refusing fights without incentives. Despite these flaws, he displays deep nobility and courage in critical moments, especially against dishonorable foes. His lecherous nature drives him to pursue women, though only Bibimba develops genuine affection for him. Initially dismissive, he gradually reciprocated her feelings, culminating in their engagement during the Universal Tag Tournament and eventual marriage. They have a son, Mantaro Kinniku, whom Kinnikuman raises as a devoted, albeit bumbling, father. To grant Mantaro a normal childhood, Kinnikuman concealed his heroic past, erasing all records of his achievements, inadvertently spoiling Mantaro and leaving him unprepared for future threats.

Relationships shape his growth. Terryman evolves from an early rival into his closest friend and tag-team partner, forging an unbreakable bond of trust. Robin Mask transitions from a fierce competitor to a respected ally, with their rivalry enduring until their eventual match in "Farewell, Kinnikuman!".

His abilities include superhuman strength and regenerative healing, often complicated by clumsiness. Key techniques involve the Kinniku Flash and Kinniku Beam from his kaiju-fighting days, and later wrestling finishers like the Kinniku Buster, Kinniku Driver, Muscle Spark, and FuuRinKaZan. Tag-team moves such as Muscle Docking (with Terryman) and the Cross Bomber (with Robin Mask) highlight his collaborative prowess. Aging significantly diminishes his physical capabilities; by "Kinnikuman Nisei," he loses most muscles, develops a large stomach, and can no longer safely execute high-impact moves. He adapts by relying on grapples, submissions, and tactical knowledge.

During the "Survivor Match for the Kinniku Throne" arc, Kinnikuman proves his right to rule by defeating five pretenders, learning of his long-lost brother Ataru Kinniku. After ascending as king, he periodically returns to Earth, such as in the "Kessen! Shichinin no Seigi Chōjin vs. Uchū Nobushi" special, leading seven justice chojin to defend Planet Rakka from the Space Samurais led by Black King. This mission underscores his leadership role among justice chojin, leveraging friendship and unity to overcome adversaries.

In later life, Kinnikuman balances royal duties with mentoring his son Mantaro, supporting him through conflicts like the dMp (Demon Manufacturing Plant) crisis. Despite his aged physique, his strategic insight remains intact. He occasionally demonstrates resilience, such as during the Choujin Olympics Revival, where he regains some physical form.