(CNN) — Mikhail Gorbachev -- the last leader of the former Soviet Union from 1985 until 1991 -- has died at the age of 91.

Gorbachev died after a long illness, Russian state news agencies reported.

"Mikhail Sergeevich Gorbachev died this evening after a severe and prolonged illness," the Central Clinical Hospital said, according to RIA Novosti Tuesday.

The man credited with introducing key political and economic reforms to the USSR and helping to end the Cold War had been in failing health for some time.

With his outgoing, charismatic nature, Gorbachev broke the mold for Soviet leaders who until then had mostly been remote, icy figures. Almost from the start of his leadership, he strove for significant reforms, so the system would work more efficiently and more democratically. Hence the two key phrases of the Gorbachev era: "glasnost" (openness) and "perestroika" (restructuring).

"I began these reforms and my guiding stars were freedom and democracy, without bloodshed. So the people would cease to be a herd led by a shepherd. They would become citizens," he later said.

From farm labor to party's rising star

Gorbachev had humble beginnings: He was born into a peasant family on March 2, 1931 near Stavropol, and as a boy, he did farm labor along with his studies, working with his father who was a combine harvester operator. In later life, Gorbachev said he was "particularly proud of my ability to detect a fault in the combine instantly, just by the sound of it."

He became a member of the Communist Party in 1952 and completed a law degree at Moscow University in 1955. It was here that he met -- and married -- fellow student Raisa Titarenko.

During the early 1960s, Gorbachev became head of the agriculture department for the Stavropol region. By the end of the decade he had risen to the top of the party hierarchy in the region. He came to the attention of Mikhail Suslov and Yuri Andropov, members of the Politburo, the principal policy-setting body of the Communist Part of the Soviet Union, who got him elected to the Central Committee in 1971 and arranged foreign trips for their rising star.

In 1978, Gorbachev was back in Moscow, and the next year he was chosen as a candidate member of the Politburo. His stewardship of Soviet agriculture was not a success. As he came to realize, the collective system was fundamentally flawed in more than one way.

A full Politburo member since 1980, Gorbachev became more influential in 1982 when his mentor, Andropov, succeeded Leonid Brezhnev as general secretary of the party. He built a reputation as an enemy of corruption and inefficiency, finally rising to the top party spot in March 1985.

'A man one can do business with'

Hoping to shift resources to the civilian sector of the Soviet economy, Gorbachev began to argue in favor of an end to the arms race with the West.

However, throughout his six years in office, Gorbachev always seemed to be moving too fast for the party establishment -- which saw its privileges threatened -- and too slow for more radical reformers, who hoped to do away with the one-party state and the command economy.

Desperately trying to stay in control of the reform process, he seemed to have underestimated the depth of the economic crisis. He also seemed to have had a blind spot for the power of the nationality issue: Glasnost created ever-louder calls for independence from the Baltics and other Soviet republics in the late 1980s.

He was successful in foreign policy, but primarily from an international perspective, with other world leaders taking note. Former British Prime Minister Margaret Thatcher called him "a man one can do business with."

In 1986, face to face with American President Ronald Reagan at a summit in Reykjavik, Iceland, Gorbachev made a stunning proposal: eliminate all long-range missiles held by the United States and the Soviet Union. It was the beginning of the end of the Cold War.

He was awarded the Nobel Peace Prize in 1990 "for his leading role in the peace process which today characterizes important parts of the international community."

The pact that resulted, the Intermediate-Range Nuclear Forces Treaty, endured as a pillar of arms control for three decades until, in 2019, the United States formally withdrew and the Russian government said it had been consigned to the trash can.

Hard-liners revolt

While Gorbachev's arms control agreements with the US could be seen as also being in the Soviet interest, the breakaway of some of the countries of Eastern Europe, followed by German unification and NATO membership for the new unified Germany (West Germany had previously been in NATO), angered old-school Communists.

In August 1991, hard-liners had had enough. With Gorbachev on vacation in the Crimea, they staged a revolt. Boris Yeltsin, the president of the biggest Soviet republic -- Russia -- and a fierce critic of what he considered Gorbachev's halfway reforms, nevertheless came to his rescue, facing down and defeating the coup plotters.

But across the Soviet Union, republics -- one after another -- were declaring independence and on December 25, 1991, Gorbachev resigned as Soviet president. As he read his resignation speech, Gorbachev defined what likely will be his legacy: "The country received freedom, was liberated politically and spiritually, and that was the most important achievement."

The red flag that flew over the Kremlin, symbol of the USSR, was lowered. The Soviet Union -- was over and Yeltsin was in control. "We are living in a new world," Gorbachev said.

In April 2012, CNN's Christiane Amanpour asked Gorbachev whether he had engineered the collapse of the Soviet Union.

Gorbachev said there had been nothing in his speeches "until the very end" that had supported its disintegration: "The breakup of the union was the result of betrayal by the Soviet nomenklatura, by the bureaucracy, and also Yeltsin's betrayal. He spoke about cooperating with me, working with me on a new union treaty, he signed the draft union treaty, initialed that treaty. But at the same time, he was working behind my back."

In 1996 Gorbachev ran against Yeltsin for the Russian presidency but got less than 1% of the vote.

Speaking out post-presidency

Three years later, Gorbachev lost the love of his life -- his wife of 46 years, Raisa -- to cancer. The couple had one daughter, Irina. "In the worst moments I was always very calm and balanced. But now that she's gone -- I don't want to live. The central point in our lives is gone," he said.

But Gorbachev did go on, speaking out on nuclear disarmament, the environment, poverty -- and in his wife's memory, set up with the family the Raisa Gorbachev Foundation to fight children's cancer.

Previously, he had established the Green Cross -- to deal with ecological issues -- and the International Foundation for Socio-Economic and Political Studies, or Gorbachev Foundation. In 2011, Gorbachev also launched the annual "Gorbachev Awards" to celebrate "those who have changed the world for the better."

Gorbachev's involvement in Russian politics continued as well. He was head of the Social Democratic Party of Russia from 2001 until his resignation in 2004 over conflicts with party direction and leadership.

In 2007, he became head of a new Russian political movement -- the Union of Social Democrats, which in turn set up the opposition Independent Democratic Party of Russia.

He told CNN's Christiane Amanpour in 2012 that he agreed Russian democracy was "alive" but added: "That it is 'well'... not so. I am alive, but I can't say that I'm fine." He explained that the "institutions of democracy are not working efficiently in Russia, because ultimately they are not free."

Mixed legacy

In an interview with CNN in 2019, Gorbachev said the US and Russia must strive to avoid a "New Cold War" developing despite worsening tensions. "This might turn out to be a hot war that could mean the destruction of our entire civilization. This must not be allowed," he said.

And asked about the demise of the 1987 treaty he signed with Reagan, Gorbachev expressed a hope that such arms control agreements could be revived.

"All the agreements that are there are preserved and not destroyed," he said. "But these are the first steps towards destruction of [that which] must not be destroyed in any case." The ultimate goal of arms control, he added, must be to get rid of nuclear weapons completely.

Gorbachev's post-USSR life also included some surprises as he worked to raise money for his causes with appearances in advertisements for Pizza Hut and Louis Vuitton. In 2004 Gorbachev won a Grammy Award for best spoken word album for children for "Prokofiev: Peter and the Wolf / Beintus: Wolf Tracks," which he recorded with former US President Bill Clinton and actress Sophia Loren.

Other awards included the 2008 Liberty Medal from the US National Constitution Center and Russia's highest honor, the Order of St. Andrew, which was given to him on his 80th birthday in 2011 by then-Russian President Dmitry Medvedev.

But to the end, Gorbachev was a leader more respected in other countries than at home. In Russia, he was reviled by some for destroying the Soviet empire and by others for moving too slowly in freeing his nation from the grip of communism. In the West, however, he remains the Nobel Peace Prize winner who helped end the Cold War.

Correction: This story has been updated to reflect that Gorbachev died at 91.

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