In the late 1930s and early 1940s, two remarkable physical phenomena — the fission of heavy nuclei and the chain fission reaction — were discovered, implying that a new powerful source of energy (nuclear fission energy) might become a practical possibility for mankind. At that time, however, the political situation in the world made the development of the atomic bomb the main objective of nuclear energy research in the countries involved. The first atomic bombs, notoriously used in the war against Japan, were produced by the United States of America only six and a half years after the discovery of fission. Four years later, the first Soviet atomic bomb was tested. This was a major step toward the establishment of nuclear parity which led to stability and global peace and thus greatly influenced the destiny of human kind. Based on documentary materials covering the period from 1939 to 1949, this paper traces the origin and evolution of the physical ideas behind the first Soviet atomic bomb and discusses the most important events associated with the project.