The Watchers are powerful beings. They possess incredible technology and believed that it was their duty to protect the universe from harm. The Watchers gave nuclear technology to another race of aliens called Prosilicans but they used the nuclear technology for war. The Watchers were very disappointed and vowed that they would never interfere with any events and to just observe and record.
The Watchers often came into conflict with the Celestials because of their different way of judgment. The Celestials believed that if the race couldn't keep up with their genetic standards, they would use force to seal the planet and give the good people a chance to reform. The Watchers believed in just observing and recording and not just kill an entire race because they didn't reach the Celestial's standards.
It has been observed that the Watchers enter a state of consciousness (fugue) in which they appear to be uploading memories to their collective, and at that time are not observing and are unaware of their surroundings. This happens every three years for exactly 42 minutes. It has also been stated that some believe the Watchers to be infinite aspects of a single, powerful entity (although this contradicts the concepts of rogue Watchers and last of the Watchers, which has often been used in other stories).
In this reality, the cruel Hawk-God committed genocide on the Watchers, leaving only one named Uilig alive. Uilig was able to get the cosmic beings to punish the Hawk-God for his crime.
Silver Surfer (1998)
In the Silver Surfer animated series, Uatu is the last of the Watchers. Originally, the Watchers observed and collected information on their home planet, which would eventually be renamed the Universal Library, with all the information they had collected. Disobeying their vows, the Watchers created a miracle cure that saved billions, but in the process it caused them all to become the Virals, organisms with primitive appearances by enhanced minds that connected all of them into a single consciousness.
Being the last of his kind, Uatu felt responsible for them and returned to them with new knowledge when he could.