Who they were
Vajiravudh (1881–1925), a son of Chulalongkorn (Rama V), reigned from 1910 to 1925. Educated in England at Sandhurst and Oxford, he was the first Siamese king educated abroad.
What they did
He articulated a Thai nationalism built on the triad of “nation, religion, king” and founded the Wild Tiger Corps (1911), a royalist paramilitary movement. The surname act of 1913 required family surnames, and he introduced compulsory primary education. In 1917 he founded Chulalongkorn University — Siam’s first university, named for his father — and brought Siam into the First World War on the Allied side, sending an expeditionary force to France, a step commonly assessed as helping later treaty revisions. A prolific writer, playwright and translator, including of Shakespeare, he published under many pen names. His spending and the rising bureaucratic elite are commonly assessed to have left fiscal strain and quiet discontent, and an unsuccessful palace plot against him in 1912 foreshadowed constitutionalist currents.
Legacy
The triad of nation, religion and king remains a core state formula, and Chulalongkorn University and the surname system endure. He died in 1925 and was succeeded by his younger brother Prajadhipok.