Celestials are powerful cosmic beings created by the First Firmament. The Celestials rebelled against their creator and Aspirant counterparts in a war that shattered the first universe into the first multiverse. The Celestials are involved in the creation of new universes, including that of the Prime Marvel Universe.
New Celestials may be born by consuming the mass of the Black Galaxy, a place made out pure biological and organic matter, or with planets which were implanted with Celestial eggs/embryos at the core and after millions of years they would be born and would consume the planet, similar to the Celestials of Earth X.
What is a celestial?
“A Celestial, like a god?” “Mmm, small ‘g’, son. At least, when I’m feeling humble.” The Celestials are the oldest race in the universe.
The standard Celestial life cycle takes eons to complete, from seeds to Emergence. Arishem mandated that some Celestials must be born every few million years. A Celestial is “born” with a colossal armored humanoid shape, bursting out of its planet in a cataclysmic manner.
The Celestials are involved in the creation of new universes, including that of the Prime Marvel Universe. The Celestials visit planets—in what is known as Celestial Hosts—to experiment on, and judge, lower life-forms. They create Eternals and Deviants from selected species.
The Celestials are immensely powerful beings featured in the Marvel Comics universe, considered by some to be villains (confirmed as such in a few official works, where they have fought heroes and villains alike, they are greatly feared even by a being of Galactus ‘ might – although in others Galactus has engaged and defeated them).
What are celestials’bodies made of?
It has been reported that the Celestials’ bodies are modular, made up of thousands of varied objects and beings. It has also been reported that they may combine to create larger more powerful amalgams and can animate severed limbs and even their computer-ware is sentient.  Celestials’ armor can be taken off.
Why did the Celestials create the Eternals?
To stop their rogue creations, the Celestials then created new synthetic beings, the Eternals, sending them across the cosmos to eradicate the Deviants and protect sentient life on the planets seeded with Celestials. “These stones, it seems, can only be brandished by beings of extraordinary strength.