Race: Mysterious Being

Age: Unknown

Gender: Male

Location: Under the earth's crust

Abilities: Superhuman Strength

Weapons: Lava Swords

Affiliation: Mother Earth

Debut: Chapter 4/Episode 1

The Subterranean King is the king of the Subterranean People. He led his people from below the surface to conquer the area on it.

(Source: One-Punch-Man Wikia)