The last leader of the Soviet Union, Mikhail Gorbachev, is being lauded as a peacemaker upon his death at 91. Yet eulogies that omit his partnership with President Reagan — and the unique way they found a path to peace — diminish his full legacy.

The Communist Party selecting Gorbachev was a surprise even to him. Its thinking, however, was that his reforms would prime the country’s moribund economy to compete with the economic juggernaut that Reaganomics had unleashed.

Without the Reagan component, would the politburo have chosen an establishment candidate? It was the usual way they handled succession, but those old boys hadn’t been lasting long in the job.

When asked why he had not held a summit with the leader of the USSR, Reagan shrugged and said, “They keep dying on me,” but the joke concealed deep frustration and disappointment.

Unlike the warmonger painted by his detractors, files from the Joint Chiefs of Staff — now declassified — show the president put off the briefings on nuclear war plans until 13 months after inauguration, unwilling to contemplate the carnage.

This was a president determined to make peace, but he was dancing alone until history served up Gorbachev at Geneva, Switzerland, in November 1985.

Reagan was a charmer and he employed parables and stories in the way no president had since Lincoln. He needed these skills to have any hope of, as Margaret Thatcher described it at his funeral, “inviting enemies out of their fortress and turning them into friends.”

The challenge at that first summit was greater than Reagan might’ve imagined, with Gorbachev viewing him as a “class enemy” with a “caveman” thinking, according to politburo transcripts.

Yet when the president invited Gorbachev for a lakeside walk, just the two with translators, Gorbachev said the word required to get peace started: Yes.

Along the way, the pair ducked into a boathouse to shake off the cold and Reagan asked —  according to his secretary of state, George Shultz, in 2009 — what has to be the strangest question upon which the fate of the world has ever hinged: Would the USSR help America if space aliens attacked?

Reagan had gotten the idea from the 1951 film “The Day the Earth Stood Still,” and invoked it for a speech before the United Nations. Members of his administration had tried to remove it from his speech, as they had with the “tear down this wall” line at Berlin, but he knew best.

Gorbachev said he would fight the Martians and Reagan agreed. It was a mutual defense treaty between mortal enemies against an imaginary foe, yet it changed the course of history.

Fred Kaplan, describing these details in his book about America’s nuclear arsenal, “The Bomb,” writes that from that moment “the atmosphere between the two men lightened, turned cordial. … When the summit ended, the two leaders released a joint statement declaring that a nuclear war ‘cannot be won and must never be fought.’”

It was the first step on the road to ending the Cold War, and to freeing the people suffering under Soviet communism. Gorbachev, of course, hadn’t planned to collapse the system or tear down the Berlin Wall.

Yet the roar for freedom proved too loud to ignore, and when the people in the Eastern Bloc rose up to claim their birthright as citizens of Earth, Gorbachev didn’t slaughter them as his predecessors would have.

By that point, he’d been awarded the Nobel Peace Prize. Although the committee snubbed Reagan, erasing him from the picture the way Joseph Stalin did foes, the two leaders are forever fixed in history.

There’s Reagan standing in Red Square with his arm around Gorbachev’s shoulder, declaring the “Evil Empire” description was from “a different era.”

Today, with the world again split between East and West, Gorbachev’s life reminds us to seek our common humanity, and that disagreements can be settled without bombs if only we can find partners for peace.

After all, as Abraham Lincoln said, “Do I not destroy my enemy when I make him my friend?” Gorbachev was willing to be Reagan’s friend, and for that, the world can be grateful for his life.