King Nangklao Memorial Day is observed in Thailand every March 31 to honor King Nangklao, also known as Rama III, who ruled from 1824 to 1851. His ascension to the throne was notable as he was the son of a concubine rather than a queen, which deviated from traditional succession practices. During his reign, King Nangklao reestablished diplomatic relations with Western countries and supported the British in the First Anglo-Burmese War with the Thai fleet and elephants. He also introduced Western medical practices to Thai doctors and is recognized for his business acumen and support of Chinese culture. This memorial day commemorates his contributions to the development of Thailand and is part of a series of memorial days celebrating the country's monarchs.