Much happens to Dr. David Bowman on his voyage. First, he and his fellow astronaut Dr. Frank Poole discover that their ship's sentient computer, Hal 9000, is not being honest with them. When Hal kills everyone else on board, Bowman disables the computer. He then is left all alone in space. Bowman is then informed of the true nature of his mission. He is to investigate a monolith on the surface of Titan that received a signal from a similar monolith that was found on the moon. He journeys on to the monolith and is transported through the Star Gate to a distant part of the galaxy.
What happens next to Bowman is not entirely clear. He finds himself in a mock-up of a hotel room on Earth. Something strange then happens to him. His corporeal body is destroyed, and he undergoes a mysterious transformation. An advanced species of alien that long ago found a way to convert their consciousness into pure energy does the same to Bowman. He becomes a "Star Child" and enters a continuum of this alien species. He is now immortal, incorporeal, and able to travel vast distances in an instant. Bowman goes back to Earth. As he arrives, he encounters a nuclear weapon on its way to its intended target. Using his newfound power, Bowman is able to easily detonate this weapon while it is still in the air, saving mankind from self-destruction.