Former Soviet President Mikhail Gorbachev died on Tuesday “after a serious and long illness,” according to the Central Clinical Hospital.

He was 91 years old at the time. It was not immediately clear what caused the death.

Gorbachev will be buried next to his wife, Raisa, in Moscow’s Novo-Dyevitchiye cemetery, according to Russia’s state-run news agency Tass.

Gorbachev was the Soviet Union’s final leader before it disintegrated. From 1985 to 1991, he was the Communist Party of the Soviet Union’s general secretary and the country’s sole president, a title he assumed in the final months of his presidency.

His rise in the 1980s, when he was young and energetic, signaled a new spring for what was then one of the world’s two superpowers. Gorbachev, a political insider with an eye to the outside world, initiated radical reforms that resulted in a series of unintended consequences.

Gorbachev was born in the southern Russian village of Privolnoye in 1931 to a peasant family who lived in a house with dirt floors. Two of Gorbachev’s grandfathers were arrested and exiled as a result of Josef Stalin’s “Terror.” During World War II, Nazi troops overran their village.

As a teenager, Gorbachev worked on the farm with his father and was awarded the Order of the Red Banner of Labor, one of the USSR’s highest honors, for a record harvest.

Gorbachev rose quickly through the ranks of the Soviet Communist Party after graduating from university in Moscow. Yury Andropov, the powerful head of the KGB, was drawn to his energy and brought him back to Moscow as a protégé.

By that time, the Soviet superpower was in trouble: the centrally planned economy was rotting, and the Soviet Union’s lag behind Western countries was becoming increasingly apparent.

The Soviet Union’s gerontic leadership exemplified the country’s decay. Gorbachev was appointed to the Politburo at the age of 47, making him nearly two decades younger than his colleagues.

Konstantin Chernenko died in office in 1985, the third elderly leader to die in office in as many years, and Gorbachev became general secretary, ignoring a succession challenge.

He shattered the Iron Curtain between the Soviet Union and the West by establishing relations with the United States, agreeing to a series of crucial summits soon after taking power.

Gorbachev signed treaties to reduce the size of his country’s nuclear arsenal, and he withdrew troops from a nine-year war in Afghanistan, a well-received policy reversal.

Gorbachev signed the Intermediate-Range Nuclear Forces Treaty with Reagan in 1988, eliminating both countries’ stocks of intermediate and short-range land-based missiles capable of carrying nuclear warheads. It was the first treaty to outlaw an entire class of weapons systems and established unprecedented protocols for both nations’ observers to verify the destruction of their missiles.

Gorbachev emphasized the invention of nuclear weapons as a “material symbol and expression of absolute military power,” as well as the fact that mankind’s survival and self-preservation were on the line.

Domestically, Gorbachev was known for two things: greater transparency and freedom, known as glasnost, and bold economic reform, known as perestroika.

It was not a winning combination in the end.

Glasnost gave the Soviet people a sense of liberation and empowerment, and when his economic policies failed, they were not afraid to express their disappointment.

Gorbachev’s vision was to give communism legitimacy by giving it a democratic face. What he didn’t seem to realize was that his people would begin to demand the genuine article.

President Joe Biden issued a statement that said, in part, “Mikhail Gorbachev was a man of remarkable vision. When he came to power, the Cold War had gone on for nearly 40 years and communism for even longer, with devastating consequences. Few high-level Soviet officials had the courage to admit that things needed to change. As a member of the Senate Foreign Relations Committee, I saw him do that and more.”