The Celestials are Jack Kirby. For a long time, they were inscrutable beings, the personification of an inevitable disaster that could doom Earth. That was before Marvel completed ruined the characters, turning them into a joke.
First appearing in the pages of The Eternals #2, in 1976, the Celestials heralded Jack Kirby's return to Marvel Comics after four years spent working for DC (where he created the Fourth World saga and the New Gods). The space gods perfectly represent Kirby's style and his unbound imagination, which was best expressed in the context of epic sagas mixing sci-fi and mythology. They were opposed by Thor, his fellow Asgardians, and the Eternals, but to no avail, the power of the Celestials was too great. The Earth was saved only by the intervention of the goddess Gaea, who offered 12 of the best humans as a gift for the space gods.
This story happened in the pages of Thor vol. 1 #300 from Mark Gruenwald, Ralph Macchio, Keith Pollard, and Gene Day in 1980, and it did a great job in portraying the Celestials as an inevitable catastrophe. They were too powerful, and even the gods could not begin to comprehend them. Flash forward in 2018, and the first story arc in Jason Aaron's Avengers run begins with dead Celestials raining from the sky. 2020's King in Black event begins with the symbiote god Knull killing three Celestials at once. Timeless, from 2021, portrays a version of Infinity Gauntlet #5 (1991) by Jim Starlin, Ron Lim, and Josef Rubinstein, as the Mad Titan had become the supreme being by collecting all the Infinity Gems. It was meant to be a shocking moment, because the Celestials, together with the other supreme beings of the Marvel Universe, were meant to be above "regular" heroes and villains.
The reason why the Celestials have lost most of their credibility is that Marvel tried to explain who and what they are. Several retcons have revealed their origins as the "angels" of the First Cosmos, the first iteration of the universe, who survive the periodical cycle of death and rebirth of the Multiverse. They also have a stronger connection with Earth: one Celestial called the Progenitor, infected with a space parasite known as the Host, crashed on the planet and, from his diseased bodily fluids, essentially created superpowers.
The problem is that all this background makes the Celestials lose their aura of unfathomable superiority. They were space gods: impossible to understand, to relate, or to reason with. Their motivations and origins should remain inscrutable. Instead, now the Avengers are using a Celestial corpse as their base, and even Dracula can kill one. By overusing the Celestials, and trying to explain them too much, Marvel Comics has simply ruined its best villains.
