On October 30 1961, the Soviet Union detonated the most powerful nuclear weapon ever built in Northern Novaya Zemlya. Its yield was 50 megatons TNT equivalent. That is equal to 1570 times the energy yield of combined yields of the bombs that destroyed Hiroshima and Nagasaki, or 10 times the yield of all chemical explosives used in WW II, one quarter of the 1883 eruption of the Krakatoa where the entire mountain exploded.
Tsar Bomba was a three-stage fusion bomb. Such bombs use a fission bomb as a primer to produce the heat and pressure necessary to detonate a secondary fusion explosion, which in turn detonates a much larger tertiary thermonuclear explosion. A 100 megaton device was planned but it was given up for because the radioactive fallout would have been too much and the plane delivering the bomb would not have had enough time to escape the explosion.
Real footage:
Here's an English language video of the test:
