As a young man, Vang Pao fought against the Japanese in World War Two. Later he led a secret war against the Communists in Laos with the backing of the US intelligence agency.
He commanded thousands of fighters in the 1960s and 1970s, disrupting Vietnamese supply lines supporting the Laotian Communist revolution.
In 1975, he fled to the US after Laos's royal rulers were ousted.
Vang Pao was a member of the ethnic Hmong minority and deeply beloved for his active defence of fellow-Hmong. Many considered him as their leader in exile.
He is credited with helping to settle tens of thousands of Hmong members in the US, as many are still persecuted and killed in isolated Laos.
However his critics accuse him of raising money from his community to fund a new rebellion in Vietnam.
He was arrested in the US in 2007 for allegedly plotting to overthrow the Laos communist government. He and nine others were detained after a lengthy federal investigation. Vang Pao was let out on bail, and charges against him were dropped in 2009.
He died Thursday surrounded by his family of complications from pneumonia. Hundreds of Hmong members are expected to attend his funeral which will be held in California.