The first atomic test had a name called "Trinity", which was detonated as a test by the United States at the Trinity site on July 16, 1945, with a yield approximately equivalent to 20 kilotons of TNT.
Some other faces you may be interested in -
1. The first thermonuclear weapon technology test of engineer device, codenamed "Mike", was tested at the Enewetak atoll in the Marshall Islands on November 1, 1952 (local date), also by the United States.
2. The largest nuclear weapon ever tested was the "Tsar Bomba" of the Soviet Union at Novaya Zemlya on October 30, 1961, with the largest yield ever seen (as of January 2016), an estimated 50–58 megatons.