EDUARD SHEVARDNADZE had been foreign minister of the Soviet Union for less than a year when the Chernobyl nuclear power plant exploded in April 1986, sending radioactive contamination into the atmosphere. Winds carried radioactive materials over Sweden and stoked international fears. At first, the new Soviet leader, Mikhail Gorbachev, was silent, and Soviet authorities covered up the scope of the disaster. But later Mr. Gorbachev admitted what happened, and the experience gave rise to his policy of glasnost, or openness. The Chernobyl experience was also searing for Mr. Shevardnadze, who wrote in his memoirs that it “tore the blindfold from our eyes and persuaded us that politics and morals could not diverge.”

To the extent that it guided Mr. Shevardnadze and Mr. Gorbachev in their “new thinking” about the world, this approach changed the course of history. Together, they abandoned the view of inexorable confrontation between two blocs and, despite fierce internal opposition, began to work with the West toward common goals. They agreed that the Soviet Union could no longer rule by threat of force and that they must find a way to ease the burden of the nuclear arms race, dramatically reversing decades of Cold War thinking.

Mr. Shevardnadze, who died Monday at age 86, was a Soviet man. He had been a Communist Party leader in Georgia, south of Stavropol, the region where Mr. Gorbachev rose to power. In a fateful conversation in 1984, during a long walk at Pitsunda on the Black Sea, they held nothing back about their troubled country. “Everything’s rotten,” Mr. Shevardnadze said. “It has to be changed.” In 1985, Mr. Gorbachev shocked the world by naming Mr. Shevardnadze his foreign minister to replace the obdurate Andrei Gromyko.

Mr. Shevardnadze and Mr. Gorbachev told leaders in Eastern Europe that Moscow would no longer dictate to them, ultimately contributing to the fall of the Berlin Wall and unification of Germany within the North Atlantic alliance. Mr. Shevardnadze helped forge the Intermediate-range Nuclear Forces agreement with President Ronald Reagan, the first treaty to eliminate an entire class of nuclear weapons. Even small and now-forgotten concessions were telling: Mr. Shevardnadze assented to the principle of on-site inspections in arms control that Moscow’s secrecy-shrouded military-industrial complex had long resisted. He was Mr. Gorbachev’s partner in a radical upending of the old order. His 1990 resignation, warning Mr. Gorbachev that “dictatorship is coming,” was another mark of conscience.

How sad it was that Mr. Shevardnadze later ignored or forgot the lessons of his own time in Moscow. His misrule as president of independent Georgia was lamentable, a time of rampant corruption and authoritarianism. But he must be remembered, first and foremost, for those fleeting but inspiring years of glasnost and new thinking at the side of Mr. Gorbachev. The two of them were improbable revolutionaries, but what they did changed everything — and millions of people are better off for it today.

A picture taken on October 10, 1986 shows Soviet Secretary General Mikhail Gorbachev (L) and Soviet Foreign Minister Eduard Shevardnadze arriving in Keflavik (Iceland), for talks with US President Ronald Reagan. (Dominique Faget/AFP/Getty Images)