Big Ivan, better known as Tsar Bomba, was 57 Megatons of Soviet might. That's 1,400 times Hiroshima and Nagasaki combined and ten times the entire combined fire power expended in WWII. In one bomb. One explosion. And, incredibly, that's only half of what it could have done.
In July 1961, Nikita Khrushchev, First Secretary of the Communist Party of the Soviet Union (and leader of the USSR) decided that he had had enough of the unspoken nuclear testing moratorium that his country, the US, and the UK had been abiding by since 1958. The 22nd Congress of the Communist Party would convene that October, providing the perfect venue to show off the USSR's military muscle. With the world's eyes on Moscow, what better way to show the West who was boss than with a "testing spectacular" setting off the largest man-made explosion of all time?