Arishem The Judge, in the comics, is the second in command of the Celestials, and in the MCU appears to be the leader. The MCU Arishem created the Eternals using the World Forge in order to reign in rogue creations of his, the Deviants, over the course of millions of years to keep populations high in order for further Celestials to be born. In the comics, Arishem headed the First Celestial Host of Earth, in which he had his other Celestials create the Deviants, the Eternals, and the Mutant X-Gene during 1,000,000 BCE.

The Arishem skin I made, the MCU version
Arishem skin I didn't make, Comic Accurate one.