Soros said he couldn’t visit Hungary under present circumstances: “It would be toxic,” he said. He told me that Orban’s campaign was “a big disappointment,” but quickly added, “I think I must be doing something right to look at who my enemies are.” Last autumn, he signaled that same sense of defiance when he announced that he was in the process of transferring the bulk of his remaining wealth, $18 billion in total at the time, to the O.S.F. That will potentially make it the second-largest philanthropic organization in the United States, in assets, after the Bill & Melinda Gates Foundation. It is already a sprawling entity, with some 1,800 employees in 35 countries, a global advisory board, eight regional boards and 17 issue-oriented boards. Its annual budget of around $1 billion finances projects in education, public health, independent media, immigration and criminal-justice reform and other areas. Organizations like Human Rights Watch, Amnesty International, the American Civil Liberties Union and Planned Parenthood are among its grantees.

Soros originally planned to close the O.S.F. in 2010. He didn’t want it to outlive him, because he feared it might then lose its dynamism and entrepreneurial spirit. But he changed his mind when he realized that, as he put it, “I had more money than I can realistically or usefully spend in my lifetime.” He also saw that, with liberal values and civil society fragile in so many places, the O.S.F.’s work was becoming ever more essential. “I found a mission, a niche, that I felt could be carried on,” he said as we finished dinner.

A few minutes later came an unexpected reminder of what he and the O.S.F. are up against. A Soros aide and I took the elevator back down together, and when we stepped into the Bristol’s lobby, we found ourselves in the middle of a reception line that stretched the length of the room. It had formed there to greet one of Africa’s longest-serving autocrats, Denis Sassou Nguesso, the president of the Republic of Congo. The next day, a few hours after Soros spoke to the European Council on Foreign Relations, Roseanne Barr went on a Twitter rant that served as a vivid demonstration of what he is up against personally. Soros was maneuvering to bring about “the overthrow of us constitutional republic,” Barr tweeted. She also claimed that Soros, a Holocaust survivor, had actually been a Nazi. Among those who retweeted the Nazi gibe was Donald Trump Jr.

According to Soros, 1944 was the formative year of his life. The Nazis invaded Hungary and immediately began deporting Jews. To save his family, his father, Tivadar Soros, a lawyer, obtained false identities for George, who was then 13, and his older brother, Paul. One day, George was ordered to deliver summonses on behalf of the Jewish Council. Tivadar, recognizing that they were essentially deportation notices, instructed his son to tell the recipients not to heed them. Soon after, Tivadar arranged for Paul to move into a rented room and sent George to live with a Hungarian agricultural official, who passed him off as his Christian godson. The official’s job included taking inventory of a confiscated Jewish-owned property; he took George with him. These episodes have become the basis for the claim that George was a Nazi collaborator. In fact, though, there is no credible evidence that he collaborated with or was sympathetic to the Nazis. George, his brother and his parents all survived the war. Soros says that he came out of the experience with a strong defiant streak, a contempt for tribalism and a propensity to side with the oppressed.

In 1946, as Communists were rising to power in Hungary, Soros fled to England. He earned a degree from the London School of Economics, where Karl Popper was a professor. In 1945, Popper published a political treatise, “The Open Society and Its Enemies,” a fierce assault on totalitarianism, in both its fascist and Marxist forms, and a ringing defense of liberal democracy. Soros left Popper’s classroom with not only the idea that would later animate his philanthropy but also the desire to live a life of the mind. He had to make money first, though. When he moved to New York in 1956 to take a job on Wall Street, his goal, he told me, was to sock away $100,000 in five years, which would allow him to quit finance and turn to scholarly pursuits. But instead, he quipped during our dinner, “I overperformed.”

In 1969, Soros formed what would become the Quantum Fund. It was one of a new breed of investment vehicles known as hedge funds, which catered to institutional investors and wealthy individuals and which used leverage — borrowed money — to make huge bets on stocks, bonds, currencies and commodities. Quantum was wildly successful from its start, delivering 40 percent annual returns. Soros would later attribute his knack for playing the markets to what he called his “theory of reflexivity” — basically, the idea that people’s biases and perceptions can move prices in directions that don’t accord with the underlying reality. Soros claimed his strength as an investor was in recognizing and acting on what he referred to as “far from equilibrium” moments. (His oldest son, Robert, once claimed the “reflexivity” explanation was bunk; he said the tip-off for his father that the market was nearing a major move was when his bad back flared up.)