'Vua Thanh Thai' (成泰帝) (Nguyen Phuoc Buu Lan) was the 10th Emperor of the Nguyen Dynasty.

He was born Prince Nguyen Phuoc Buu Lan, Thanh Thai was the son of Emperor Duc Duc. When Emperor Dong Khanh came to power, Prince Buu Lan was put under house arrest with his mother for having connections with those who opposed him. When Dong Khanh died however, the French colonial authorities and the high-ranking Mandarins decided that Buu Lan was the ideal successor. After the murder of Emperor Duc Duc, the boy's mother cried when her son was taken away, fearing that he would meet the same fate. Instead he was enthroned as the new Vietnamese Son of Heaven; Emperor Thanh Thai.

Even at the age of 10 Thanh Thai was recognized as being very intelligent and was already realizing that the French were keeping watch over him through palace spies. Also, whereas Dong Khanh had tried to be friendly with the French, Emperor Thanh Thai took a course of passive-resistance. Although he refrained from outright rebellion (which would have been political suicide) he made his feelings clear in other ways, symbolic gestures and biting remarks. He was also a man of the people, and a monarch who cared deeply for his country. The Emperor would often slip out of the Forbidden City dressed in the clothes of a poor commoner to talk with his people directly and see how they were being effected by government policies.

To show that he was friendly with western civilization, Emperor Thanh Thai was the first Vietnamese monarch to cut his hair in western style and learn to drive a car. He encouraged French-style education but maintained bitter feelings over their control of his country. He also supported numerous building projects and took an interest in the everyday lives of his subjects. When traveling among his people he would hold what Americans would call "Town Hall meetings" with the Emperor seated on a mat with his subjects in a circle around him, discussing the issues of the day and hearing their point of view.

Slowly, as the Emperor began to realize how thoroughly his palace had been infiltrated with French spies he had to feign insanity to escape their constant scrutiny. With his enemies believing he was a harmless lunatic Thanh Thai was able to work more forcefully for Vietnamese autonomy while waiting for the right time to throw off colonial rule. He was on his way to join a resistance movement in China when he was arrested by the French who declared him insane and forced the Emperor to abdicate.

In 1907, his son was installed as Emperor Duy Tan of Vietnam. Thanh Thai was exiled first to Vung Tau and when Duy Tan rebelled against the French they were both exiled to Reunion Island in 1916. He never gave up hope for the liberation of his country and in 1945, he was allowed to return home but was kept under house arrest in Vung Tau, South Vietnam. He died in Saigon on March 24, 1954.