Kang the Conqueror is human, but the answer is not as straightforward as we would have liked, as there are numerous versions of this time-traveling warlord, and some of them have been alien in origin. But the answer still stands, the main version of Kang from Earth-6311, Prime Kang, is human.
In other words the Celestials are still under Kang though not weaker or lesser than him.
The Celestials existed way before Kang and his variants, and given the role of the TVA and Kang's variant He Who Remains, it all points at the Celestials not being aware of Kang and the TVA, but the latter know that the Celestials exist.
Eternals gave a deeper look at what the Celestials can do and the power they have in the Marvel Cinematic Universe, but there might be one character more powerful than all of them: Kang the Conqueror, and here's why.
Some readers mistakenly refer to Kang as a descendant of Reed, but that's incorrect. As Fantastic Four #273 (1984) established, Kang is a descendant of the family Nathaniel Richards started after he migrated to Earth-6311. While Kang is related to Reed, he's a descendant of Reed's half-brother Arthur.
Kang has arrived, and if the hype is to be believed, he's going to be even worse than Thanos. Now that we've officially met the character in Ant-Man and the Wasp: Quantumania, here are a few reasons Kang is a better villain than his MCU predecessor.
Kang vs. Thanos: Who is stronger? Kang is stronger than Thanos, with the Conquerer being much more challenging to defeat than the Infinity Gauntlet-wielding villain.
History. Dormammu allied himself with Baron Mordo, Abomination, Cobra and staged an attack against their former master Kang the Conqueror, several years after Kang had conquered the world. Kang found himself unable to defeat Dormammu and fled back to prevent the formation of this reality.
Kang the Conqueror may be the strongest villain in the MCU yet. But one Eternal can stop him if he can survive long enough to face him. Kang's growing presence in the Marvel Cinematic Universe has inadvertently disadvantaged many of its heroes before they've even met him.
Kang the Conqueror will take center stage in the former, while The Beyonder is reputed to be the main villain in Secret Wars. With all this in mind, it's likely that Galactus will be the next Thanos-level threat after Kang. Kang the Conqueror made his MCU debut in the Disney+ series Loki.
We know from Guardians of the Galaxy 2 that Celestials are god like beings. Odin seems to possess a power far beyond any other Asgardian. He was a celestial that, unlike Peter's dad, used his power to birth a race of people who each carried a bit of his power within them.
Celestials are powerful cosmic beings created by the First Firmament.
Ego was a celestial born outside of the influence of another celestial (i.e. he wasn't born of a celestial seed like the ones we now know are) and thus, lacked the typical physical form of one.
His divine origins and his status as "the God of Strength" make Hercules so powerful that he can rival or surpass even the mightiest Avengers such as Thor or Hulk. However, the Prince of Power has another, more subtle, ability that turns out very useful against masters of time travel such as Kang.
Galactus: Who Wins? Galactus wins easily in combat against Kang. While Kang's Battle Armor and other technology have proven to be quite useful in fights against the Avengers and the Fantastic Four, nothing in his arsenal would help him defeat the Devourer of Worlds.
Kang is usually known for going after greater stakes than anything that Moon Knight is usually involved in, but Moon Knight has defeated him before. Kang was trying to gather Khonshu's totems for himself, and Moon Knight, with the help of past versions of himself, was able to defeat the time-traveling villain.
Avengers: Endgame heavily features time travel, with Tony Stark being the mastermind behind it. Because of his understanding of time travel, the theory states, Kang is fearful that Iron Man could take him down.
He asks Scott Lang (Paul Rudd) whether he had killed him yet, since he murdered countless Avengers during his multiversal conquests. That made me realize that Kang already killed Iron Man, Black Widow, Gamora, Loki, and Heimdall in Endgame and Infinity War.
Kang the Conqueror vs. Scarlet Witch, who wins? As you can see, Kang and Wanda are pretty evenly matched. However, based on everything we've stated, Wanda's powers are a bit more versatile as she can utilize a variety of types of magic, including countering every single power that Kang has.
Although Kang the Conqueror is being set up for a dynamic future in the MCU, it seems as though Loki's He Who Remains was actually more powerful.
As a time traveler from the 31st century, Kang has access to technology and weaponry far beyond anything that 21st century Earth is capable of producing. With the resources at his disposal, Kang possesses mastery over time and space, as well as the power to battle armies single-handedly.
Kang isn't physically stronger than Thanos, and if the two were to square up in a one-vs-one fight then the Titan would arguably win. However, Kang's knowledge of the multiverse means that would quite literally be several steps ahead of Thanos at all times.
Jonathan Majors plays Kang the Conqueror in Ant-Man and the Wasp: Quantumania. If you know your Marvel comics, that sentence doesn't make a whole lot of sense. After all, Kang is an Avengers-level threat, so why was he chosen as the villain for the third Ant-Man movie?
One where Ahura was saved and rejoined his Inhuman family, but another where he stayed with Kang. In the second timeline, Ahura eventually betrayed Kang and murdered him, taking possession of his armor and becoming the new Kang the Conqueror.
It's worth noting that even with Thanos' mastery of the Infinity Stones, they are of little use when facing Kang the Conqueror. Kang has the power to manipulate time and timelines to such an extent that even the most powerful artifacts in the universe are rendered ineffective.