They were unlikely soldiers.

The small band of middle-aged art experts, artists, educators and architects who signed up during World War II to join President Franklin D. Roosevelt’s program to protect and secure European art treasures were on a mission to find the paintings, sculptures and other cultural touchstones stolen by the Nazis for their art-obsessed Führer.

The group’s phenomenal success and heroism were so little-known that those involved were close to being a historical footnote. Instead, their story is now a feature-length motion picture, The Monuments Men, opening nationally today.

The film, directed by and starring George Clooney, who also shares screenwriting and producer credits, drew an A-list cast, including Matt Damon, Cate Blanchett, Bill Murray, John Goodman, French actor Jean Dujardin and British actor Hugh Bonneville — the star of PBS’ Downton Abbey. Clooney, Damon, Blanchett and Dujardin are all Oscar winners.

But the real force behind the story isn’t Clooney or any of the other Hollywood heavyweights — it’s Robert M. Edsel of Dallas.

The movie is based on his book The Monuments Men: Allied Heroes, Nazi Thieves and the Greatest Treasure Hunt in History.

He is, as he often acknowledges, an unlikely champion.

Edsel is a former professional tennis player and a successful oil and gas executive, but no art historian. After selling his energy company, he moved his family to Europe in the mid-1990s for the experience. He soon became passionate about the art around him and how it had survived the war.

The result was a single-minded pursuit to learn how the men and women of the program — known as the Monuments, Fine Arts and Archives Section of the Civil Affairs and Military Government Sections of the Western Allied Armies —rescued 5 million pieces of art, centuries of culture produced by da Vinci, Michelangelo, Vermeer, Rembrandt, Renoir and others.

Jewels of the art world were found hidden in salt mines and even in castles. They had been taken from the walls of museums and from the homes of collectors, many of them Jewish.

In an interview, the dapper 57-year-old Edsel, tall and slender with a mane of distinctive white hair that he keeps unfashionably long, recalled that he stumbled across the back story of the obscure art protectors while living in Florence, Italy.

“I was crossing the Ponte Vecchio, the only bridge in Florence that wasn’t destroyed in the war, and I wondered, ‘How did so many works of art survive?’ ” he said, recalling the moment in 1997 as he crossed the medieval span over the Arno River.

The answer came over the ensuing years and at a steep personal financial cost.

“We passed $1 million a long time ago,” said the very driven, very intense Edsel.

He has written three books about the art rescue; co-produced a documentary, The Rape of Europa; created the Monuments Men Foundation, which helps repatriate recovered art and advocates for congressional recognition of the Monuments Men legacy; and consulted on the movie based on his book.

He began by looking for photographs of the historic discoveries made by the Monuments Men, researching files in the labyrinth of the National Archives facility in College Park, Md. It stores every aspect of U.S. history, including war records.

‘Pinch-me’ moments

Now he is hanging around with movie stars.

“There are ‘pinch-me’ moments every day during this process,” he said.

Edsel was at the film’s gala New York City premiere Tuesday, then was off to Europe for a screening at the Berlin International Film Festival on Saturday with, as he puts it, “George and Matt and whoever else is going,” followed by stops in various European cities.

Accompanying the group will be Harry Ettlinger, 88, of New Jersey. He is one of only five Monuments Men — four American men and one British woman — still alive out of a force of 345 from 13 countries. Crucial to the effort were the 120 Americans who helped find and repatriate the stolen art.

Many returned to the U.S. to careers in museums and the arts and were very elderly by the time Edsel found them. But he interviewed 17 of them — 15 men and two women — before a dozen died.

Granger at screening

Edsel screened the film at the National Archives in Washington last week.

The audience included Lynda Bird Johnson Robb, daughter of former President Lyndon Johnson, and her husband, Chuck Robb, a former Virginia governor and U.S. senator.

Edsel co-hosted a screening the night before in the U.S. Capitol’s new auditorium with Rep. Kay Granger, R-Fort Worth, one of his earliest supporters. She is leading an effort to honor the Monuments Men with the Congressional Gold Medal, the nation’s highest civilian honor.

“These men and women were asked to do a remarkable thing by going into harm’s way to save and return stolen works of art and other cultural items,” Granger said. “It used to be that ‘to the victor goes the spoils,’ but the Monuments Men made sure that European art and cultural history wasn’t lost to the hands of Hitler and the destruction caused by the war.”

Coincidence or not, the screenwriters used her name for Damon’s character — “James Granger.”