The Watcher is an enigmatic extra-terrestrial in Marvel Comics' universe. He is a member of an immortal, almost omnipotent race of aliens known only as the Watchers. The Watchers are sworn to never interfere with the development of the universe, only to observe. This oath stems from an incident that occurred millions of years ago, when the Watchers gave advanced technology to a primitive race. The Watchers left these aliens to their own devices for several years; when they returned, the race had completely self-destructed in a nuclear war. Ever since, the Watchers are sworn to an oath of non-interference.

Uatu, generally known simply as "The Watcher" to humans, was the first member of this race to be seen. He first appeared in Fantastic Four #13 (1962), created by Stan Lee and Jack Kirby.

Uatu, the Watcher assigned to observe the Earth's solar system, dwells on the "Blue Area" of the Moon, an abandoned city built by the alien Kree centuries ago. In his first appearance, he encountered the Fantastic Four and their enemy, the Red Ghost , as the latter entered his home; he repelled the invader with a thought and, breaking his oath for the first time, revealed himself to the Fantastic Four. Uatu, being youthful and rebellious in comparison to his brethren, would break his oath many more times in the future, most notably in Fantastic Four #48, in which he tried, and failed, to prevent the Silver Surfer from bringing the world-devourer Galactus to the Earth.

Uatu has appeared countless times since, on several occasions narating other characters' adventures. He also served as narrator for the What If...? series, which told tales of alternate versions of the Marvel Universe where certain events unfolded differently (and often disastrously). At least once, he has been removed from his duty as Watcher of the Earth, but he nevertheless returns to his true calling, observing the world he has become so fond of. In particular, he considers the Fantastic Four to be quite intriguing; Reed Richards could be said to be his only human friend.

In the mini-series 1602 we learn that, although FF #13 was the first time he broke his oath, the anomalous appearance of Marvel's superheroes more than 300 years early forced him to severely bend it, communicating with the 1602 version of Doctor Strange following the latter's death (thereby following to the letter his commandment not to reveal himself to a living soul). To remind him of this, he must maintain a pocket universe containing the 1602 world within himself.