Subterranean People

The Subterranean People (地底人, Chitējin) are the self-proclaimed "True People of the Earth". They are ruled by the Subterranean King and live under the earth's crust, but grew too numerous in numbers and planned to take over the surface. They were eventually stopped and chased back into the ground by Saitama.

Overview
The Subterranean People have a humanoid appearance. They are very large with hands the size of a regular human's head. They only have two toes on each feet, and three fingers on their hands. They wear golden or metallic ornaments, wristbands, necklaces and armor over their right shoulder. They all wear different metal helmets, with only their round eyes showing.

The Subterranean People seemed rather confident in their ability to take the Earth for themselves, but after the Subterranean King was defeated they retreated quickly, showing their cowardice.

Saitama Introduction Arc
Saitama wakes up in his apartment when a hand comes through his wall and grabs him, he punches the arm, but for some reason it has no effect. The arm then punches Saitama and sends him flying into a wall, which along with him fly out into the street. Suddenly one of The Subterranean People comes out of the ground behind Saitama and punches at him, he attempts to block, but gets sent flying into a guard rail, which he bounces off and collides with an overpass. When Saitama stands up his forehead is bleeding and he sees more of the Subterranean People climbing out onto the street. The Subterranean People then proclaim their ownership of the earth and a fight ensues, with Saitama eventually becoming the victor. At that point the Subterranean King shows up, but before anything could come out of that Saitama wakes up.

Shortly after Saitama wakes up the Subterranean King shows up, but is defeated instantly after which the Subterranean People retreat back to the Earth.