Warning! Spoilers for King in Black: Symbiote Spider-Man #5
Not much is known about Marvel’s mysterious Uatu the Watcher, including his actual species, and Uatu himself only adds to the mystery. Case in point - King in Black's most important tie-in just revealed that Uatu could very well be a horse.
King in Black: Symbiote Spider-Man by Peter David takes place many years before Knull’s current invasion in Marvel’s main timeline. Set during Spider-Man’s tenure with his black symbiote suit, this mini-series has Kang the Conqueror attempting to save the future by journeying to the past, hoping to find a way to kill Knull before he reaches his full power. Kang’s first order of business was abducting Uatu the Watcher, a nigh-omnipotent cosmic being sworn to observe but not interfere with the goings-on in the universe. In trying to harvest Uatu’s knowledge, however, Kang simply allows the Watcher to see the future and all the catastrophic events that await, but this turns out to be a blessing in disguise.
Fast foward to issue #5, Kang, Spidey, and a rag-tag group of heroes find themselves on Knowhere searching for Black Knight’s ebony blade, which is crucial for the coming conflict. Uatu helps the heroes recover the weapon, after which he joins them in a nightclub to explain everything to a very confused Spider-Man. Peter asks Uatu to sit for the lengthy conversation, but Uatu states that he always stands. Spider-Man then likens the Watcher to a horse; a comparison Uatu agrees with. “Except you’re not a horse,” Spidey says, to which Uatu simply replies, “How do you know?”
While this line was obviously meant as a joke to play off Peter’s abundant confusion, it also highlights how little anyone really knows about Marvel's cosmic observers. The Watchers are mysterious beings gifted with nearly infinite knowledge and incredible psionic power, yet they are forbidden from ever using it for anything beyond observation. Even Uatu’s minimal involvement in the events of this mini-series got him barred from traveling to the future by the rest of his order. In a way, perhaps Uatu is a horse in the metaphorical sense - forced to simply carry the burden of knowledge without being able to use it. Then again, he could also be an actual horse who uses his cosmic powers to shape-shift. Can’t rule it out.
Kidding aside, the mysteriousness of the Watchers is a big part of what makes them so interesting. Marvel strives to keep Uatu’s true nature a secret because that’s a core aspect of his character, even if he does wind up interfering with Earth more often than he should. Plus, the secrecy allows Marvel to make readers question - even for a second - whether or not the all-powerful observer is really just a horse, and that has to count for something.