Navajo Code Talker Samuel Billison, who served on the Navajo Nation Council and was the longtime president of the Code Talker Association, has died.

The Navajo Nation said he died Wednesday of heart complications. His age was not immediately known.

Billison joined a group of Navajo Marines – the Code Talkers – who invented a military code based on the Navajo language to confound the Japanese during World War II. They used the code and their native language to communicate troop movements and orders.

The Marines developed a secret vocabulary that renamed military armaments and equipment using rough equivalents in Navajo.

Airplanes became birds, ships became fish, and weapons were named after various items. For example, the word “bomb” was replaced by the Navajo word for “egg.” Amphibious units were designated “chal,” or frogs.

Billison said he joined the U.S. Marines right out of high school in 1943. When the Marines realized he was fluent in Navajo and English, they assigned him to become a code talker.

“It was a code that was within the language,” he said in a recent interview with the Associated Press. “So a regular Navajo that didn’t study that code had no idea what we were talking about even though it was their language.”

Billison and his fellow Code Talkers were not allowed to discuss their work when they returned home after the war.

“When we were being discharged the Marines told us, ‘If anybody asks you what you did with the Marines, just say you fought. Don’t say anything about radio, about code or communication,”‘ Billison said.

The Defense Department first released information on the Code Talkers in 1968.

Billison traveled throughout the world to carry the story of the Code Talkers, who “offered their language to allow the citizens of the United States the freedom that we are able to enjoy today,” Lawrence Morgan, speaker of the Navajo Nation Council, said.

Billison earned a doctorate from the University of New Mexico in Albuquerque, served on the Navajo Nation Council, and helped reorganize the education system under the Bureau of Indian Affairs.

He never stopped advocating for veterans and young people, and recently helped in the tribe’s Get Out the Vote campaign.

“In particular, the Code Talkers targeted the youth,” Morgan said. “The message they shared was that they fought for our rights as citizens, including the right to vote.”