In Watchmen, Alan Moore and Dave Gibbons utilize the comic form to provide commentary on a number of political issues of the time, including the Vietnam War, anti-Reaganism, and the Cold War and anxiety surrounding nuclear weapons. There is one character specifically whose personal journey in intrinsically tied to the theme of nuclear devastation: Jon Osterman, also known as Dr. Manhattan. Dr. Manhattan represents the anxieties around nuclear weapons from a personal, political, and philosophical perspective.
Jon is sixteen years old when the US drops the atomic bomb on Hiroshima and Nagasaki. Upon hearing of the power of the atomic bomb, Jon's father (a watchmaker) encourages him to become an atomic physicist. After earning a PhD in atomic physics from Princeton University, Jon goes on to work at Gila Flats. While working there, Jon accidentally gets trapped inside a test chamber during an experiment tampering with the "intrinsic fields" of objects. His body is vaporized in the chamber, but instead of dying, he reassembles his body "in the right order" and discovers that he has gained the ability to "control atomic structures."
Even though Jon attempts to return to a normal life, his entire existence is unmitigatedly altered by the experiment. His body has a humanoid structure but with blue skin and blank white eyes. His physical appearance and his emotional engagement with the world are forever altered.
Later in the comic, Jon is also perceived as a radioactive threat and asked to leave the Earth. The changes in his physique represent the trauma caused by nuclear weapons on the survivors of nuclear attacks: genetic mutations, emotional trauma, and reduced quality of life.
In addition to personal trauma, Jon also represents the political implications of nuclear weapons. After the US government discovers his ability to "control atomic structures," they make him a part of the American defense strategy. He is renamed Dr. Manhattan, after the Manhattan Project, and inspires more fear even than the atom bomb, because his consciousness gives the US the ability to be more strategic about utilizing the destructive powers of atomic fission. He interferes on behalf of the US in the Vietnam War, which helps the US win the war. Dr. Manhattan's presence alters the historical timeline and acts as a reminder that atomic power is ultimately destructive.
Dr. Manhattan also symbolizes the philosophical implications of nuclear threat. When he suffers the trauma of the accident, his connection to time is inexplicably severed. He does not experience time in a linear moment-to-moment fashion anymore. Instead, his past, present, and future are rendered into a constant present. Chapter 4, which tells his story, is not written in a linear fashion but in a disjunctive, disrupted manner, providing images from different times even within the same frame. Due to his separation from linearity, Dr. Manhattan also loses his connection to humanity. After humans' fear of him forces him to flee to Mars, his conversation with Laurie reveals that he feels disconnected from both Laurie and humanity in general. It is only when the story of Laurie's true parentage is revealed that Dr. Manhattan feels some connection to human reality and agrees to save the human race. Dr. Manhattan's separation from humanity is a result of two factors: the changes in his own perception of reality and the growing fear he inspires in humans. He represents the fear that the destructive potential of the atomic bomb might separate humans from their moral compass.
Watchmen culminates in a tragedy, but not one of the nuclear kind. Because Laurie is able to reestablish Dr. Manhattan's severed connection to humankind, he agrees to return to Earth to find New York City destroyed in a utilitarian attempt to avert World War III. He saves Earth by vaporizing Rorschach before he can expose Veidt, and Dr. Manhattan ultimately leaves Earth to find a less complicated galaxy, making the declaration that "nothing ever ends."