Mikhail Gorbachev, the last president of the Soviet Union and who helped end the Cold War, died on Tuesday. He was 91.

Gorbachev, who served as president from 1985 to 1991, died after a long illness, according to Russian state media.

"Mikhail Sergeevich Gorbachev died this evening after a severe and prolonged illness," RIA Novosti reported.

Gorbachev, who adopted the principles of glasnost and perestroika, introduced political and economic reforms, while forging weapons reduction agreements with the U.S. as well as partnerships with western powers. His unlikely friendship with U.S. President Ronald Reagan helped end the Cold War.

In 1989, Gorbachev refrained from using force as pro-democracy protests swept across Soviet-bloc nations. He also ended the Soviet Union's disastrous war in Afghanistan.

In 1990, he won a Nobel Peace prize for his role in ending the Cold War.

"I like Mr. Gorbachev. We can do business together," former British Prime Minister Margaret Thatcher once said of the Soviet Leader. "We both believe in our own political systems. He firmly believes in his; I firmly believe in mine. We are never going to change one another. So that is not in doubt, but we have two great interests in common: that we should both do everything we can to see that war never starts again, and therefore we go into the disarmament talks determined to make them succeed."

After leaving office, Gorbachev maintained some public presence before his health reported began to decline in 2011 and then later stopped international travel in 2015.

He drew condemnation in 2014 for defending the Crimean status referendum. The move led to Russia's annexation of Crimea.

Born in the village of Privolnoye, Gorbachev adhered to Marxism–Leninism before trending towards social democracy.

He married in Raisa Titarenko, who died in 1999. The couple had one daughter.