Celestials

Celestials are immensely powerful beings, considered by some to be villains. Worshiped as 'space gods' by many races, they may be benevolent by their own lights, but they have absolutely no regard for the interests of anyone but themselves. They consider virtually all other beings 'germs', and destroy entire worlds and species if they think it necessary. Even the Watchers are not safe from their judgment.

Appearance
Celestials are gigantic armor-clad humanoids. They are approximately 200 feet tall, some of them are even larger.

History
The origins of the Celestials have always been vague, but it is known that they have visited Earth on at least 4 occasions (known as Hosts) during which they would alter and exterminate many of Earth's natives. They created both the Eternal and Deviant offshoots of humanity, as well as sinking Atlantis underneath the Ocean.

They have done this on many worlds throughout the universe, experimenting with life using entire planets as petrie dishes and mercilessly pruning the life forms they deem unworthy or useless. The ultimate goal of all this remains unknown. Nevertheless, they are not entirely deaf to placation; Thor and Susan Storm have both communicated with the Celestials. The Celestials. along with many of the Marvel Universe's abstracts, are killed by the Beyonders. they fight the enigmatic aliens with all their power, but are all destroyed
 * Powers and abilities: the powers of the Celestials are for all intents and purposes limitless. When Odin, the head of one of Earth's most powerful pantheons, had decided to stand up to them. Working together with the heads of the other god families such as Zeus and Vishnu, he created a mighty weapon, the famous Asgardian Destroyer; when the Celestials reappeared on Earth, Odin animated  the automaton with the life-force of all Asgardians except for Thor and confronted the space gods wielding the deadliest weapon in the world, the Odinsword. But the Celestials handily dealt with this ultimate attack as if it were a mere distraction.

Notable Acts of Villainy
Although an amoral race of super-entities rather than true villains the Celestials have created dangerous artifacts and engaged in acts that some would consider immoral - usually to try and manipulate evolution in some fashion or to "purge" unwanted genetic codes from planets they are "progressing".
 * creation of the Death Seed.
 * Celestial technology is utilized by Apocalypse (though illegally so, since he was apparently punished by them over this over time)
 * regular "purge" of worlds deemed "failures" of genetic manipulation (amounts to mass-genocide / planetary destruction)
 * as a side-effect of a war between Celestials and the Godheads of Earth the Destroyer armor was forged.
 * the creation of Terminus is a result of an act of vengeance by an alien race on the Celestials, who judged them "unfit" for existence.
 * a group of Celestials encountered Galactus, who warned them he knew of their "true purpose" - this caused them to fly into a violent frenzy and try to destroy him, suggesting their true nature is sinister in nature.