Mr. Winton is shown here in an undated family photograph with one of the children he rescued. (PA/Press Association Images)

“Who’s helping the children?”

That was the question that Nicholas Winton, a 29-year-old English stockbroker, asked when he found himself in Prague in 1938. As war loomed in Europe, humanitarian groups had initiated efforts to help Jews, political refugees and other groups endangered by Hitler’s advancing threat. But Mr. Winton found no such effort underway specifically for the children of Czechoslovakia.

Inspired by the Kindertransport, a rescue operation then in place for children in Germany and Nazi-occupied Austria, Mr. Winton set about a mission he called his “wartime gesture.” He was credited with saving, through his personal initiative, the lives of at least 669 boys and girls. For decades after the war, he kept his work secret.

By the time of his death July 1 at 106, Mr. Winton was internationally celebrated as a hero of the Holocaust. He often was described as a British Schindler, a reference to the German industrialist Oskar Schindler, whose efforts to rescue 1,200 Jews were dramatized in director Steven Spielberg’s 1993 film “Schindler’s List.”

Mr. Winton appeared uncomfortable with the honors bestowed on him, which included a knighthood from Queen Elizabeth II, and remarked that the work accounted for “just nine months in a very long life.”

Mr. Winton receives the Order of the White Lion in Prague in 2014. (Michal Cizek /AFP/Getty Images)

Those nine months began in December 1938. By that time, European powers had signed the Munich Agreement, which allowed Nazi Germany to annex the Czech territory known as the Sudetenland. British Prime Minister Neville Chamberlain predicted that the agreement would bring “peace for our time.”

Mr. Winton was preparing for a ski trip when he received a call from his travel companion, Martin Blake.

“The skiing’s off,” Mr. Winton later recalled his friend saying. “I am off to Prague instead. I have a most interesting assignment and I need your help. Come as soon as you can. And don’t bother bringing your skis.”

Blake, a schoolteacher, was associated with the British Committee for Refugees from Czechoslovakia, an organization created to assist Jews and other targets of Nazi persecution who left the Sudetenland after the German occupation.

“I called myself Honorary Secretary of the Children’s Section of the British Committee for Refugees from Czechoslovakia,” Mr. Winton told The Washington Post in 1989. “The other people,” he said, referring to government bureaucrats and others confronted with his doggedness, “they just called me a bloody nuisance.”

Mr. Winton occupied a hotel room in Prague’s Wenceslas Square and later an office where, over several weeks, he collected applications from parents seeking a way out of Czechoslovakia for their children. Thousands of families lined up outside his door, according to an account by the U.S. Holocaust Memorial Museum.

“Each group felt that they were the most urgent,” Mr. Winton told the London Daily Mail. “How could I, or anyone else in London, choose the most urgent cases? Often it was heartbreaking.”

With the applications in hand, Mr. Winton returned to England and began seeking host families for the children. He wrote letters to government leaders around the world, including in the United States. Nearly all of them turned down his requests for assistance. “If America had only agreed to take them, too,” he said, “I could have saved at least 2,000 more.”

Sweden agreed to take in some of the young refugees, as did Britain — provided that Mr. Winton could identify families willing to care for the children until they were 17. The government also required that he secure the staggering sum of 50 pounds per child for their eventual return home.

Many of the children would lose their parents in the Nazi death camps and had no home to return to after the war.

While holding down his job at the stock exchange and with help from assistants, including his mother, Mr. Winton gathered or forged travel documents for the children, raised the necessary funds and recruited host families through newspaper advertisements and other means.

In Czechoslovakia, he had the foresight to photograph the children looking for homes. To prospective host families, those haunting images proved more compelling than a list of names.

“It was a nasty, commercial way of doing things,” Mr. Winton told an interviewer years later, “but it was effective.”

The host families came from Jewish, Christian and other religious backgrounds. Decades after the war, Mr. Winton recalled the resistance he encountered from some rabbis, who perhaps at that time did not fully realize the degree of danger facing the Jews of Europe.

“One day, a couple of rabbis arrived at my home and said that they understood that some of the good Jewish children whom I was bringing over to this country were going to Christian homes,” he told the London Daily Telegraph. “And that must stop, they told me. And I said: ‘Well, it won’t stop. If you prefer a dead Jew in Prague to a live one who is being brought up in a Christian home, that is your problem, not mine.’ ”

The first group left Prague by air March 14, 1939, one day before Nazi Germany invaded the Czech areas of Bohemia and Moravia. Seven subsequent transports — the last departed Aug. 2, 1939 — carried the children by train through Europe and then by ship across the English Channel.

Mr. Winton said he saw them only briefly at London’s Liverpool Street railway station before they were collected by their new families.

“Inside I was cheering like a football match, but outwardly I was calm and quiet,” he told the Observer, a British publication, years later. “I knew that for every Jewish child safely deposited on the platform that day, there were hundreds more still trapped in Czechoslovakia. And I knew that because I was organizing this emigration entirely on my own, I wouldn’t be able to bring out a fraction of those in such terrible danger.”

The last train was scheduled to depart Sept. 3, 1939, carrying about 250 children — the largest of Mr. Winton’s transports, according to the Daily Mail. But Germany had invaded Poland two days earlier, war was declared and the borders were closed. None of the children slated to leave on that train are believed to have survived.

“Terrible,” Mr. Winton said. “It doesn’t bear thinking about.”

According to the Holocaust Museum, Mr. Winton was born Nicholas Wertheimer (other sources say Wertheim) on May 19, 1909, in West Hampstead, England. His parents, who were of German Jewish ancestry, baptized him in the Anglican Church and changed the family name to Winton. He said he was not religious.

Asked whether he helped the Czech children because of his heritage, Mr. Winton told the London Evening Standard: “That’s for a psychologist to answer. I didn’t do it consciously because I had any Jewish blood in me. . . . When I set out to try to bring children in from Czechoslovakia, I didn’t do it because they were Jewish children. I did it because they were children.”

During the war, Mr. Winton worked as a Red Cross ambulance driver in France and in England during the London Blitz. He later joined the Royal Air Force. After the war, he involved himself in humanitarian activities, including refu­gee assistance, overseeing the sale of Nazi loot, distributing the proceeds to Holocaust survivors and handling monetary loans in the recovering nations of Europe.

He also raised money for British organizations benefiting the elderly and the disabled and co-owned a popsicle factory before retiring in 1967.

In the late 1980s, Mr. Winton’s wife, the former Grete Gjelstrup, was rooting through the attic when she came upon a scrapbook containing documents related to the wartime rescue effort. He had never mentioned it to her.

“I suppose there are quite a number of things that husbands don’t tell their wives,” Mr. Winton told Matej Minac, who directed several films about the story, including “All My Loved Ones” (1999), “The Power of Good: Nicholas Winton” (2002) and “Nicky’s Family” (2011).

The scrapbook made its way to Elisabeth Maxwell , the Holocaust scholar and wife of newspaper magnate Robert Maxwell. Soon Mr. Winton found himself featured in British newspapers and on the BBC television program “That’s Life!”

“May I ask, is there anyone in our audience tonight who owes their life to Nicholas Winton?” the host, Esther Rantzen, inquired. “If so, could you stand up, please?”

To Mr. Winton’s shock, everyone around him rose.

Four of Mr. Winton’s “children” grew up to become Karel Reisz, the director of films including “The French Lieutenant’s Woman” (1981); Alfred Dubs, a prominent Labor Party politician in Britain; Joe Schlesinger, a noted Canadian journalist; and Dagmar Simova, a cousin of former U.S. secretary of state Madeleine Albright.

Another, Vera Gissing, wrote a book about Mr. Winton and said that he had saved “the major part” of her generation of Czech Jews.

Mr. Winton’s wife died in 1999 after five decades of marriage. Their youngest son had Down syndrome and died in childhood. Survivors include two children, Nick Winton and Barbara Winton; and two grandchildren.

Mr. Winton’s death was announced on the Web site of the Rotary Club of Maidenhead, England, of which he was a former president. He lived in Maidenhead and died at a hospital in Slough, Berkshire. The cause was not immediately available.

Mr. Winton once reflected on his “wartime gesture” and why he had made it.

“Why do people do different things?” he told an interviewer. “Some people revel in taking risks and some go through life taking no risks at all.”