King Naresuan Day is observed in Thailand every April 25 to honor Naresuan the Great, a revered monarch known for liberating Siam from the Taungoo Empire's vassalage. He was the 18th king of the Ayutthaya Kingdom and is celebrated for his military achievements, including successful defenses against invasions and the expansion of Ayutthaya's influence. The day commemorates his death on April 25, 1605, during a war with Burma, and it was officially established as a holiday by the Thai government in November 2005. Observances typically include state ceremonies that reflect on Naresuan's legacy and contributions to Thailand's history. Additionally, Royal Thai Armed Forces Day, celebrated on January 18, also honors Naresuan's military prowess, particularly his famous victory in an elephant duel against the Burmese viceroy.