Chester Nez, the last of 29 Navajo Indians who helped create a code used during the second world war and never broken by the Axis powers, has died aged 93.
Flags are being flown at half-mast until Sunday on the tribe's territory in the US.
"The power of our language was shared with the world when the original 29 Navajo Code Talkers stepped forward for service," Navajo Nation president Ben Shelly said.
He said Nez's passing in his sleep on Wednesday "closes another chapter in the annals of Navajo".
Nez and 28 other Navajos were recruited by the Marine Corps in May 1942 to create a communications code for the battlefield based on their complex tribal language, which is tonal and unwritten. He later participated in the war's Pacific battles in Guadalcanal, Guam, Peleliu and Bougainville.
Nez's death "sadly marks the end of an era in our country's and Marine Corps' history", said Marine Corps spokesman Colonel David Lapan. "The Navajo Code Talkers made invaluable contributions to the war effort in the Pacific theatre."
Last year, Nez said: "I was very proud to say that the Japanese did everything in their power to break that code but they never did."
A total of 400 Navajo Indians took part in the Pacific war as Code Talkers.
The Navajo code attributed an Indian word for each letter of the alphabet. So "moasi," which means "cat", designated the letter "c".
The code wasn't declassified until the 1980s because the military hoped it could be reused.