(Uatu) Fantastic Four #13 (1963); (as species) Strange Tales #53 (1964)
Their home-world exist in an unknown galaxy, far beyond the Milky Way Galaxy. It was covered with lush vegetation and bears no signs of inteligence life or habitation.
The Watchers possessed advanced technology existing billions of years before most other species. They used their advanced technology to create temporary dwellings which they disassemble after use. They also possess technology to observe alternate realities.
Ruled under leader The One.
The Watchers are humanoid beings, that dress in the clothing resembling cloathing of ancient monks or priest.