The superman exists, and he's American

-- Watchmen's Earth, America, 1959

With these (somewhat ominous) words, Dr. Manhattan was introduced to the public. 6 feet tall, square-jawed and a light shade of blue, Jon Osterman - now known as Dr. Manhattan (due to the Manhattan Project's association both with high technology and a horrible, deadly weapon) - is a victim of a lab accident, becoming trapped in a test chamber where the "intrinsic field" was being removed in an attempt to discover the Unified Field Theory. The removal of this field disintegrated Dr. Osterman in the first Planck time unit of switching on the device.

This was a bit of a setback for Jon, however not much of one as within a few weeks, his disembodied and quite Unified consciousness managed to figure out how to put his physical self back together from spare atoms everywhere - his interest in watchmaking while he was young (before his father pushed him into nuclear research after the bomb was dropped on Hiroshima in 1945), dealing with intricate parts of a system undoubtedly helped. While he was doing that, he also figured out how to affect everything around him in the same manner. To all intents and purposes, this made Dr. Manhattan into a superhero, or a god, able to perform supernatural deeds with a thought.

In the universe of the Watchmen, the 1960s are (mirroring real life) a time of cold war, nuclear apprehension, rampant McCarthyism and two-sided propaganda, and the constant threat of mutually assured destruction - having seen Dr. Strangelove recently, I had to double-check that I wasn't confusing the two stories together; there's even a war room sequence with projected casualties and losses of a first strike scenario. Into this atmosphere of fear and uncertainty comes the superweapon Dr. Manhattan, as he is publicized and his abilities demonstrated far and wide in the hopes that it's obvious which superpower has the real upper hand. It is during these demonstrations (and from snippets of Jon's life in the previous chapters) that we, the readers, get the feeling that Jon doesn't really understand either the purpose of the demonstration, nor the effect of his powers on the Soviets (unease, fear, increase rather than decrease of paranoia) - the affairs of humans are becoming insignificant to him.

He does manage to win the Vietnam War for the USA, however.

During the further events of the Watchmen, Jon became subjected to increasing emotional trauma as his sea change manifested in subtler ways. Becoming analytical and logical as only a supreme being divested of morality can be, but holding on to the innate human curiosity, Jon's personal and social life falters and withers away. Unable to relate to other humans, the drives, wants and needs of people around him (including his lovers) become a complete and utter enigma. While his superior intellect is aware of the effect and wishes to halt or at least delay his separation from humanity, he is unable to resynchronize with the feelings of what is to him another species to be observed, a curiosity just as intriguing and remote as the interactions of subatomic particles.

The final effect of the experiment was to unstick Jon from the human perception of time. Throughout the book (although quite notably in the part of it devoted entirely to him) it was obvious that while his actions were rooted within normal human time, his perception was aware of his entire existence. Unable to change what he constantly knows is going to happen - despite having enough raw power to do so - and tired of warring with the dichotomy of wanting to be human but at the same time quite content in being what he is, Jon eventually leaves Earth for "galaxies less complicated" in 1985.

From the start of his existence to the end of the book, the disintegration of Jon's humanitas is as heartwrenching as it is complete.
A small list of powers Dr. Manhattan manifested during his stay on Earth:
  • Growing to giant human-shape (at least 100ft) in defiance of the Cube-Square Law
  • Lifting equipment of inestimable weight - several tons at least
  • Instant teleportation of self and others - no known limit of persons teleported (a whole mob was teleported once), no known distance limit (Earth-Mars confirmed, extra-galactic teleport planned by Dr. Manhattan)
  • Creation and destruction of objects at will - buildings, tanks, humans destroyed, a sizable glass domicile was created from sand. It is not known if Dr. Manhattan can create life, but it seems doubtful.
  • Early in his career, in a quietly understated yet poignant act where he becomes upset for the first (and, barring one other time, only) time, Jon rejects the ubiqutous symbol of Bohr's atom as his SuperIdentiMark™ helmet, and instead opts for a simple representation of a hydrogen atom (nucleus in center, 1 electron in orbit - a circle around a point, the whole surrounding the individual) on his forehead. He draws this with his finger, smoke curling gently from it - he experiences no pain. It is here that his connection to all things human starts to strain.

The graphic novel Watchmen, by Dave Gibbons and Alan Moore. Which you should read.