In 1938, Sir Nicholas Winton was an everyday stockbroker. But when Hitler's troops marched into Czechoslovakia, causing refugees to flee to Prague, Winton took notice. He canceled a planned ski vacation to Switzerland and flew instead directly to the Czech capital, armed with a plan.
He couldn't have imagined that the result would be Winton's List -- names of 669 Jewish children who owe him their lives.
"It was fairly obvious something sinister was afoot," Winton, who lives in England, told ABC News. "I don't think anybody really anticipated the real horror of what the gas chambers became."
Compelled to act, Winton chartered trains, raised money, found the children in gravest danger, forged papers and, the hardest task, found families in England to take in the children.
"All one had to do was find out whether it was possible," he said. "Well, I found out that it was possible."
The Germans had Winton under surveillance, but didn't stop him. "We were getting rid of those people Hitler wanted to get rid of," Winton said. "I mean, you even had the Gestapo at Wilson Station helping the children onto the trains."
Vera Gissing, whose parents died at the Bergen-Belsen concentration camp, was 10 years old when she and her sister boarded one of Winton's trains.
"I can still see that train slowly chugging along, you know, and our parents becoming out of sight," said Gissing, who's now in her late 70s. "It's a scene which stays forever."
When Hitler invaded Poland on Sept. 1, 1939, 251 children were boarding Winton's sixth train at Prague station, including Gissing's cousins. But, the train never left, leaving her cousins, among many other children, trapped to perish.
"They had to get off that train and go back home," she said. "I only found one solitary person who survived."
Winton joined the Royal Air Force and then returned to civilian life after the war, concealing his heroism in the face of normality. For 50 years, his actions and altruism went unrecognized, until his wife unearthed a scrapbook in their attic.
"Didn't so much keep it secret as I didn't talk about it," he said. "What do you do? Go up to someone and say, 'By the way, forgot to tell you.'"
Now, Winton's story has reached Czech classrooms, educating children about true courage and activism. Last year, one school changed its name to "Nicholas Winton School" in his honor.
"He didn't only save 669 -- he saved a generation because we've had children and grandchildren," Gissing says. "Today, there's about 7,000 of us alive."
With two children and three grandchildren of her own, Gissing has built a family, in thanks to Winton's valor.
Reflecting on his actions, Winton said it's "very gratifying that you've spent your life on earth and something good has come of it."
Sir Nicholas Winton is now 90. The Czech government nominated Winton for the Nobel Peace Prize this year, after 32,000 school children signed a petition in admiration.