When he was 18 years old, Adolfo Kaminsky worked in Paris as part of a Jewish resistance cell. His specialty was forging passports for people who would otherwise be taken to concentration camps. He did this work in part because he himself was a Jewish refugee, born in Argentina to Russian Jewish parents—and his (real) passport saved him from deportation to Auschwitz.

After WWII, Kaminsky proceeded to take his forging skills abroad, doing the same work in conflicts around the world. In a profile for the New York Times, Pamela Druckerman writes:

Though he was a skilled forger—creating passports from scratch and improvising a device to make them look older—there was little joy in it. “The smallest error and you send someone to prison or death,” he told me. “It’s a great responsibility. It’s heavy. It’s not at all a pleasure.” Years later he’s still haunted by the work, explaining: “I think mostly of the people that I couldn’t save.”

The Times also produced this short documentary about Kaminsky, who is now 91. Watch for the story of a hero who, like so many, did his work in secret.

Also worth a look: Sarah Kaminsky's TED Talk, "My Father the Forger." She has also written a book about her father.