Mikhail Gorbachev the last leader of the Soviet Union has died aged 91 reported the BBC.
Russian President Vladimir Putin expressed his deepest condolences on Mr Gorbachev's death, his spokesman Dmitry Peskov told Russian news agency Interfax, according to Reuters.
"This legacy is one we will not forget," she added.
UK Prime Minister Boris Johnson said he admired Mr Gorbachev's courage and integrity.
"In a time of Putin's aggression in Ukraine, his tireless commitment to opening up Soviet society remains an example to us all," he said.
Mr Gorbachev was the eighth and final leader of the Soviet Union, and was the General Secretary of the Communist Party of the Soviet Union from 1985 until 1991. He was also the country's head of state from 1988 until 1991, serving as the chairman of the Presidium of the Supreme Soviet from 1988 to 1989, chairman of the Supreme Soviet from 1989 to 1990, and president of the Soviet Union from 1990 to 1991. Ideologically, Gorbachev initially adhered to Marxism–Leninism, but he moved towards social democracy by the early 1990s.
Mr Gorbachev, who took over in 1985, is best known for opening up the USSR and for bringing the Cold War to a peaceful end, but he was unable to prevent his country collapsing in 1991.
Many Russians blame him and his reformist policies for the country's demise.
The hospital where he died said he had been suffering from a long and serious illness.
He will be buried in Moscow's Novodevichy cemetery, the resting place of many prominent Russians, next to his wife Raisa who died of leukaemia in 1999, Tass news agency said.