December 2, 1942
Manhattan Project: A team led by Enrico Fermi initiates the first self-sustaining nuclear chain reaction.
Enrico Fermi had been the first to use a neutron to produce the radioactive change of one element to another. On 2 December 1942 he initiated the atomic age with the first self-sustaining chain reaction, after which he became known as "father of the atomic bomb". Michael H. Hart ranked him #76 in his list of the most influential figures in history.