Mikhail Gorbachev, the last leader of the former Soviet Union, died Tuesday night at the age of 91, according to Russian state news agencies.

Gorbachev, who was credited with introducing key 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. Two key phrases of the Gorbachev era were "glasnost" (openness) and "perestroika" (restructuring).

Gorbachev had humble beginnings: He was born into a peasant family in Privolnoye on March 2, 1931. Here, he's with his parents in Privolnoye.
Gorbachev had humble beginnings: He was born into a peasant family in Privolnoye on March 2, 1931. Here, he's with his parents in Privolnoye.
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Gorbachev with his maternal grandparents, Panteley and Vasilisa Gopkalo, circa 1937.
Gorbachev with his maternal grandparents, Panteley and Vasilisa Gopkalo, circa 1937.
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Gorbachev, far right, poses for a photo with his classmates, circa 1947.
Gorbachev, far right, poses for a photo with his classmates, circa 1947.
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Gorbachev, wearing the hat, is seen with classmates in the 1940s.
Gorbachev, wearing the hat, is seen with classmates in the 1940s.
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Gorbachev, seen here in 1984, became a member of the Communist Party in 1952 and completed a law degree at Moscow University in 1955. By the end of the 1960s, he had risen to the top of the party hierarchy in the Stavropol region.
Gorbachev, seen here in 1984, became a member of the Communist Party in 1952 and completed a law degree at Moscow University in 1955. By the end of the 1960s, he had risen to the top of the party hierarchy in the Stavropol region.
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Gorbachev and British Prime Minister Margaret Thatcher pose for a picture in London as they meet in December 1984. Thatcher once called him "a man one can do business with."
Gorbachev and British Prime Minister Margaret Thatcher pose for a picture in London as they meet in December 1984. Thatcher once called him "a man one can do business with."
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Gorbachev, front center, attends an International Women's Day Gala in Moscow in March 1985. He became a full Politburo member in 1980, and he rose to the top party spot in 1985. That effectively made him the leader of the Soviet Union.
Gorbachev, front center, attends an International Women's Day Gala in Moscow in March 1985. He became a full Politburo member in 1980, and he rose to the top party spot in 1985. That effectively made him the leader of the Soviet Union.
Boris Yurchenko/AP
Gorbachev follows pallbearers carrying the casket of his predecessor as Soviet leader, Konstantin Chernenko, in Moscow's Red Square in March 1985.
Gorbachev follows pallbearers carrying the casket of his predecessor as Soviet leader, Konstantin Chernenko, in Moscow's Red Square in March 1985.
Boris Yurchenko/AP
Gorbachev and US President Ronald Reagan hold a historic "fireside chat" in Geneva, Switzerland, in November 1985. The two had a series of summit talks.
Gorbachev and US President Ronald Reagan hold a historic "fireside chat" in Geneva, Switzerland, in November 1985. The two had a series of summit talks.
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Gorbachev and Reagan attend the closing ceremony for the Geneva Summit in November 1985.
Gorbachev and Reagan attend the closing ceremony for the Geneva Summit in November 1985.
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Gorbachev and his wife, Raisa, are welcomed in Prague, Czechoslovakia, in April 1987.
Gorbachev and his wife, Raisa, are welcomed in Prague, Czechoslovakia, in April 1987.
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Gorbachev visits Bucharest, Romania, in May 1987.
Gorbachev visits Bucharest, Romania, in May 1987.
AP
Gorbachev waves during a parade in Moscow in November 1987.
Gorbachev waves during a parade in Moscow in November 1987.
Boris Yurchenko/AP
Gorbachev talks with Reagan at the beginning of a summit in Washington, DC, in December 1987.
Gorbachev talks with Reagan at the beginning of a summit in Washington, DC, in December 1987.
Boris Yurchenko/AP
Gorbachev and Reagan sign an arms control agreement in December 1987 banning the use of intermediate-range nuclear missiles.
Gorbachev and Reagan sign an arms control agreement in December 1987 banning the use of intermediate-range nuclear missiles.
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Gorbachev shakes hands with businessman — and future US President — Donald Trump at the US State Department in December 1987. It was before a luncheon held in Gorbachev's honor.
Gorbachev shakes hands with businessman — and future US President — Donald Trump at the US State Department in December 1987. It was before a luncheon held in Gorbachev's honor.
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Gorbachev shows Reagan around Red Square during Reagan's visit to Moscow in May 1988.
Gorbachev shows Reagan around Red Square during Reagan's visit to Moscow in May 1988.
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Gorbachev, bottom right, and members of the Politburo vote to remove Andrei Gromyko, bottom center, as Chairman of the Presidium of the Supreme Soviet in October 1988. Gorbachev would then succeed him in the role.
Gorbachev, bottom right, and members of the Politburo vote to remove Andrei Gromyko, bottom center, as Chairman of the Presidium of the Supreme Soviet in October 1988. Gorbachev would then succeed him in the role.
Boris Yurchenko/AP
Gorbachev visits New York with Reagan and US Vice President George H.W. Bush in December 1988.
Gorbachev visits New York with Reagan and US Vice President George H.W. Bush in December 1988.
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A Moscow woman and her cat watch Gorbachev's New Year message in December 1988.
A Moscow woman and her cat watch Gorbachev's New Year message in December 1988.
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Gorbachev and Cuban President Fidel Castro wave during Gorbachev's visit to Cuba in April 1989.
Gorbachev and Cuban President Fidel Castro wave during Gorbachev's visit to Cuba in April 1989.
Julio Etchart/Panos Pictures/Redux
Gorbachev greets East German leader Erich Honecker after arriving in East Berlin in October 1989.
Gorbachev greets East German leader Erich Honecker after arriving in East Berlin in October 1989.
Boris Yurchenko/AP
Coretta Scott King presents Gorbachev with the Albert Einstein Award for his contribution to peace in June 1990.
Coretta Scott King presents Gorbachev with the Albert Einstein Award for his contribution to peace in June 1990.
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Gorbachev gives a speech after receiving the Nobel Peace Prize in June 1991. He was awarded "for his leading role in the peace process which today characterizes important parts of the international community."
Gorbachev gives a speech after receiving the Nobel Peace Prize in June 1991. He was awarded "for his leading role in the peace process which today characterizes important parts of the international community."
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Gorbachev shakes hands with Bush, then president, in Moscow in July 1991.
Gorbachev shakes hands with Bush, then president, in Moscow in July 1991.
Rick Wilking/Reuters
Gorbachev rubs his eyes while speaking in Moscow in August 1991. He threatened to resign if the Soviet Union fell apart. That month, hard-liners in his country staged a revolt while Gorbachev was on vacation in the Crimea. Boris Yeltsin, the president of the biggest Soviet republic and a fierce critic of what he considered Gorbachev's halfway reforms, came to Gorbachev's rescue, facing down and defeating the coup plotters.
Gorbachev rubs his eyes while speaking in Moscow in August 1991. He threatened to resign if the Soviet Union fell apart. That month, hard-liners in his country staged a revolt while Gorbachev was on vacation in the Crimea. Boris Yeltsin, the president of the biggest Soviet republic and a fierce critic of what he considered Gorbachev's halfway reforms, came to Gorbachev's rescue, facing down and defeating the coup plotters.
Alexander Zemlianichenko/AP
Gorbachev held a news conference the day after he returned from Crimea in August 1991. He had been held captive in his dacha by coup plotters attempting to remove him from power in order to stop his economic reform policies. The coup leaders had stated publicly that Gorbachev was stepping down due to ill health. Here, Gorbachev holds a crumpled note that he had hidden on his body to explain what really happened in case he was killed.
Gorbachev held a news conference the day after he returned from Crimea in August 1991. He had been held captive in his dacha by coup plotters attempting to remove him from power in order to stop his economic reform policies. The coup leaders had stated publicly that Gorbachev was stepping down due to ill health. Here, Gorbachev holds a crumpled note that he had hidden on his body to explain what really happened in case he was killed.
Robert Wallis/Panos Pictures
Gorbachev closes his resignation speech after delivering it on Soviet television in December 1991. Across the Soviet Union, republics — one after another — were declaring independence. Shortly after his speech, the Soviet hammer-and-sickle flag was lowered from the Kremlin, and in its place rose the white, blue and red flag of Russia.
Gorbachev closes his resignation speech after delivering it on Soviet television in December 1991. Across the Soviet Union, republics — one after another — were declaring independence. Shortly after his speech, the Soviet hammer-and-sickle flag was lowered from the Kremlin, and in its place rose the white, blue and red flag of Russia.
Liu Heng Shin/AP
Gorbachev and Reagan spend time together at Reagan's ranch in California in May 1992. Both were no longer in power.
Gorbachev and Reagan spend time together at Reagan's ranch in California in May 1992. Both were no longer in power.
Bob Galbraith/AP
From left, Bush, Gorbachev and former German Chancellor Helmut Kohl attend a ceremony at Prague Castle in 1999. They were among six former world leaders being honored with the Order of the White Lion, the highest Czech state award.
From left, Bush, Gorbachev and former German Chancellor Helmut Kohl attend a ceremony at Prague Castle in 1999. They were among six former world leaders being honored with the Order of the White Lion, the highest Czech state award.
Michal Dolezal/CTK/AP
Gorbechev bows his head at Reagan's funeral in June 2004.
Gorbechev bows his head at Reagan's funeral in June 2004.
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Gorbachev talks to Russian President Vladimir Putin before a news conference in Germany in December 2004.
Gorbachev talks to Russian President Vladimir Putin before a news conference in Germany in December 2004.
Jochen Luebke/DDP/AFP/Getty Images
CNN founder Ted Turner and Gorbachev answer questions during a United Nations news conference in 2005. Gorbachev was presenting Turner with the Alan Cranston Peace Award later that day.
CNN founder Ted Turner and Gorbachev answer questions during a United Nations news conference in 2005. Gorbachev was presenting Turner with the Alan Cranston Peace Award later that day.
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Gorbachev shakes hands with a member of Green Cross International during a tour of New Orleans' Lower Ninth Ward in 2007. Gorbachev founded Green Cross International, an environmentalist organization.
Gorbachev shakes hands with a member of Green Cross International during a tour of New Orleans' Lower Ninth Ward in 2007. Gorbachev founded Green Cross International, an environmentalist organization.
Ann Heisenfelt/AP
Gorbachev and United Nations Secretary-General Ban Ki-moon shake hands at the UN's European headquarters in 2009. The theme that day was "resetting the nuclear disarmament agenda."
Gorbachev and United Nations Secretary-General Ban Ki-moon shake hands at the UN's European headquarters in 2009. The theme that day was "resetting the nuclear disarmament agenda."
Salvatore Di Nolfi/Keystone/AP
Gorbachev appears on stage during the finale of the Gorby 80 Gala in London in 2011. The concert celebrated Gorbachev's 80th birthday.
Gorbachev appears on stage during the finale of the Gorby 80 Gala in London in 2011. The concert celebrated Gorbachev's 80th birthday.
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