The former name of Thailand was Siam. It was changed in 1949, after the Siamese assembly voted to change it the previous year. However, this was not the only attempt to change the country's name from Siam to Thailand.
In 1939, the dictator Field Marshal Luang Phibunsongkhran tried to change the name of the country. He was unsuccessful in doing so, because the anti-axis powers were unhappy that Siam had sided with the Japanese in the war, so they did not recognize the new name. After the war, the country was successful in changing the name during the aforementioned year.