Uchuu Shounen Soran (1965)

A classic sci-fi TV anime. The adventures of super-boy. In the 21st century, a human boy is raised on the Planet Soran, home of one of the most advanced civilization in the Galactic Federaion. The planet has the gravity 15 times stronger than Earth. People of Soran changed the boy into a cyborg so that he can live on the planet. Years later the boy returns to Earth. He calls himself Soran. On Earth, his phsical ability is 15 times superior to normal humans. He uses the power for justice. (Source: AniDB)