After his accident or rebirth, he is quickly requested to work with the US government of the day where he uses his new abilities and his already enhanced knowledge in the quest to better man kind. He was rechristened Dr Manhattan after the Manhattan Project that developed the First Atomic Weapons after W W 2. In the early days he did dabble with being a Super Hero as such, but science and knowledge where his true vocation.
He has many powers that include super human strength, telekinesis, teleportation and control over matter. His mind perceives time as happening simultaneously, ie the future, present and past to him are one thing. He states that although he can see the future he cannot act to change things, he is but a passenger who's own actions have already been predetermined.
When the US Government passed a bill banning Masked Vigilantism, unlike the other Watchmen, Dr Manhattan did not have to reveal his identity as the government already knew who he was. But as far as Dr Manhattan was concerned he was no longer Jon Osterman, that person died in the accident that gave birth to him.
As the years go on he starts to lose touch with his humanity at the cost of distancing himself with others, especially his long time girl friend and lover The Silk Spectre.
Here is my take on Doctor Manhattan
More WATCH-DAWGS next time