The Atomic bomb has been the most powerful weapon of mass destruction in the world since its creation.
A group of scientists led by Robert Oppenheimer were the creators of the first Atomic bomb as a part of the top secret Manhattan project. This project started out of fears that the Nazis may be developing such weapon to be used against the Allied forces in World War II. The first atomic explosion called Trinity was successfully tested on 16 July 1945 at the Alamogordo Test Range in New Mexico, USA. This test explosion eventually culminated into the deadly atomic bombing of Japanese cities of Hiroshima (on 6th Aug 1945) and Nagasaki (on 9th Aug 1945) by the United States during the World War II, killing at least 129,000 people.
Atomic bomb becomes the deadly beast that it is, due to a nuclear chain reaction which releases humongous amount of energy. At its core this chain reaction involves splitting up of atomic nuclei of radioactive elements like Uranium and Plutonium, thereby releasing enormous energy. Although this energy can be used for constructive purposes like power generation and food preservation, the atomic bomb is probably one use of this energy which creates extremely undesirable effects.
Thankfully atomic bomb has never been used till date after the unfortunate bombings of Hiroshima and Nagasaki.