Big Five refers to the five permanent members of the Security Council of the United Nations (UN). These are China, France, Russia, the United Kingdom, and the United States. The Soviet Union held a permanent council seat until the nation broke up into a number of independent countries in 1991. That same year, Russia, which had been part of the Soviet Union, took over the Soviet seat.
Nationalist China (Taiwan) held a seat on the Security Council until 1971, when it was expelled from the United Nations. At that time, the People’s Republic of China (Communist China) was admitted to the United Nations and given a permanent seat on the Security Council.