Soldier, designated the original Kinnikuman Soldier, emerged as a brutal and merciless warrior. Born on Planet Kinniku in the same hospital and timeframe as Kinnikuman, his early life unfolded in extreme poverty, prompting his family's emigration to another planet. There, his parents were killed by a soldier, an event that fundamentally shaped his existence and instilled a lifelong motivation to hunt and eliminate soldiers across the universe.

His personality manifested as ruthless and sadistic, governed by a twisted code: he killed only individuals demonstrating a will to live, deliberately sparing those who abandoned hope. He demonstrated this philosophy by killing three survivors of an attack; after skinning two victims before the third, he explained his code. When the traumatized survivor regained his will to live, Soldier immediately executed him. Despite his brutality, he displayed naivety in judging people and significant stubbornness.

Visually, Soldier presented a militaristic appearance. He wore a sleeveless camouflage jacket, consistently carried a rifle, and bore a prominent scar crossing his left eye, contributing to his cruel facial demeanor.

Following transformation by the God of Brutality into the Kinnikuman Soldier, he received a mission concerning the Survivor Match for the Throne of Planet Kinniku. Tasked with assembling a team of brutal Choujin, he recruited members across various locations: Tail Lamp in the Netherlands, Heavy Metal after a trial by combat, The God Shark during a swimming competition, Lupin (briefly encountering resistance), Woolman in a café, and Bulldozerman in Canada as his Second-in-Command, mistakenly believed initially to be Canadianman.

He transported his team to Mt. Fuji for intensive training. There, Soldier discovered his teammates possessed unexpectedly amiable personalities, conflicting with his vision of a "Brutal team," provoking significant anger. His leadership faced a critical challenge when a mysterious challenger, later revealed as Ataru Kinniku, confronted him. Ataru effortlessly defeated Soldier's entire team. Soldier launched an enraged attack but was swiftly incapacitated by Ataru's technique. Defeated and lying in the snow, Soldier's mask was removed. Ataru donned the mask, declaring his intention to assume the Kinnikuman Soldier identity and participate in the Survivor Match. Soldier extracted a promise from Ataru to win before losing consciousness.

Soldier and his defeated teammates (Bulldozerman, Woolman, God Shark, Heavy Metal) were discovered severely injured and buried in the snow on Mount Fuji the night before the match between Team Phoenix and Team Soldier. Transported to a hospital, all except Soldier died en route. Tended by Warsman, Meat, and Terryman, Soldier revealed his identity as one of the Five Fated Princes. He recounted Ataru Kinniku's challenge on Mount Fuji, the group's defeat, and the theft of his mask, noting each teammate bore injuries forming the shape of an "A".

Recovering at Himeji hospital, Soldier witnessed Ataru Kinniku fighting on television. The sight of Ataru utilizing the "Napalm Stretch" technique—the technique responsible for his and his teammates' injuries—triggered intense panic. This reaction caused his wounds to reopen, resulting in fatal bleeding and his death.

His known technique was the Assault Driver. His career titles included Team Soldier Captain and Planet Kinniku Throne Successor Candidate. His official win/loss record in singles matches lists an unknown number of soldier kills and a loss to Ataru Kinniku via Napalm Stretch.