Dr. Manhattan is hands down the most powerful being in the Watchmen universe. He is a godlike character, who got his abilities when he, Jon Osterman, was accidently locked in a scientific test chamber. The chamber was built to conduct an experiment to see how matter was held together, and as a result Jon was torn apart on a molecular level.
Months later he rematerialized as the powerful and immortal Dr. Manhattan.
Recruited by the government, Manhattan worked closely with the military to help America win the Vietnam war, and joined other costumed heroes in their fight for justice.
With a mastery over time, matter, and teleportation, Manhattan is a powerhouse of energy, who rather sit secluded on a distant planet than interact with others. He wears the symbol of the hydrogen atom, something he believes should be respected in its simplicity.
There is an atom based hero that Manhattan resembles, and that hero is Captain Atom. Atom like Manhattan worked alongside the military to aid America against foreign threats and gained his powers because of a scientific accident. He gained the ability to fly, had super strength and the ability of transmutation or turning objects from one form to another.