Vang Pao, the former general and leader of his Hmong ethnic group in Laos, has died in exile in the US, aged 81.
He had been in hospital for about 10 days before his death late on Thursday.
As a young man, he had fought against the Japanese during World War II, and with the French against the North Vietnamese in the 1950s.
He led a CIA-sponsored secret war in Laos during the Vietnam War and, when it was lost, led many of his people into exile.
The former Central Intelligence Agency Chief William Colby once called Gen Pao "the biggest hero of the Vietnam War".
Gen Pao was a controversial figure, deeply loved by many Hmong for his insistence on freedom from foreign domination. He was also accused of subversion.
Americans who first came into contact with him found a man skilled in warfare and with the charisma necessary to sustain a dangerous 15-year long operation in support of the US against the North Vietnamese.
Last of his kind
The CIA airline, Air America, carried Gen Pao and his fighters across the country.
On the ground, he and his men disrupted Vietnamese supply lines and engaged in pitched battles to try to stave off the Vietnamese-backed communist victory in Laos.
When that effort failed in 1975, Gen Pao led many thousands of Hmong into what are now well-established exile communities in the US.
The Central Valley of California, Minneapolis and cities throughout Wisconsin have a significant Hmong presence.
"He's the last of his kind, the last of the leadership that carries that reference that everyone holds dear," said Blong Xiong, a Fresno city councilman and prominent Hmong-American.
"Whether they're young or old, they hear his name, there's the respect that goes with it."
In his later years, Gen Pao was accused of leading rebellions or sponsoring subversion against the People's Democratic Republic of Laos.
In 2007, he was charged along with nine others with plotting to use AK-47 rifles, missiles and mercenaries to overthrow the Lao government. Charges against him were later dropped.
Regarded by some as an exiled head of state, he also worked as a security guard at a supermarket.