Atom The Beginning's story takes place in Japan after a great calamity. There were two geniuses who dreamed of the future. One was Umatarou Tenma. The other was Hiroshi Ochanomizu. The two labored day and night in robot research — Tenma to create a "god," and Ochanomizu to create a "friend." Thus a robot, A106, was born from their collaborative friendship. Would A106 really become a god, or a friend? The manga and anime tell a prequel story leading up to the birth of Astro Boy.
Summary taken from: MyAnimeList