The younger brother of Tatsunori Kinniku, Sadaharu Kinniku started out life into the royal Kinniku family. He possessed a genius wrestling ability and believed himself to be superior to his brother. At the mere age of thirteen, he unconsciously performed the Muscle Spark, which killed his sparring partner in the process.

He was thus locked away in an underground dungeon and his existence erased from history. After receiving the death sentence, he escaped from prison to Mt. St. Parfait where he faced off against Mirageman. Recognising Sadaharu as the descendant of Silverman, Mirageman invited him to become reborn as the Perfect Chojin Nemesis. 

(Source: Kinnikuman Wiki)

Kinnikuman (a.k.a. Kinniku Suguru) is a cowardly, clumsy, moronic, gyuudon-devouring excuse for a superhero (or Choujin)... who just happens to be the prince of an alien planet. But despite his pathetic appearance, he is very honorable and can become quite powerful when he needs to be. With his sidekick Meat-kun and fellow Choujins Terryman and Ramenman there to help him, Suguru quests to become the greatest Choujin on the planet. Whether with a combination of tremendous heart and stamina (The Burning Inner Strength) or the "Power of Friendship", Kinnikuman frequently defeats villians 10 times more powerful than him and often causes his enemies to have a change of heart and join him. Though he seems destined to be an idiot forever, slowly but surely Kinnikuman becomes worthy of the title "Hero". 
 
Notes: 
- Between volumes 36 and 37 publication there's 22 years gap. From volume 38 onwards starts restarted in 2011 version. 
- Kinnikuman won the 30th Shogakukan Manga Award for best children's manga in 1984.

The second season of Kinnikuman: Kanpeki Choujin Shiso-hen.