George Smith, one of the Navajo code talkers who helped the U.S. military outfox the Japanese during World War II by sending messages in their obscure language, has died, the president of the Navajo Nation said.

“This news has saddened me,” Ben Shelly, the Navajo president, said in a post Wednesday on his Facebook page. “Our Navajo code talkers have been real life heroes to generations of Navajo people.”

Smith died Tuesday, Shelly said, and the Navajo Nation’s flag is flying at half-staff until Sunday night to commemorate his life.

Several hundred Navajo tribe members served as code talkers for the United States during World War II, using a military communications code based on the Navajo language. They sent messages back and forth from the front lines of fighting, relaying crucial information during pivotal battles like Iwo Jima.

Military authorities chose Navajo as a code language because it was almost impossible for a non-Navajo to learn and had no written form. It was the only code the Japanese never managed to crack.

The Navajo code talkers participated in every assault the U.S. Marines carried out in the Pacific between 1942 and 1945.

The code talkers themselves were forbidden from telling anyone about the code — not their fellow Marines, not their families — until it was declassified in 1968.

Now in their 80s and 90s, only a handful of code talkers remain.

“They have brought pride to our Navajo people in so many ways,” Shelly said. “The nation’s prayers and thoughts are with the family at this time as they mourn the passing of a great family man who served his country and protected his people.”

Shelly’s Facebook post didn’t mention Smith’s age or the cause and location of his death. A statement about the death on the official Navajo Nation website was not accessible late Thursday.