Thai Sa

Sanphet IX (Thai: สรรเพชญที่ ๙) or Thai Sa (Thai: ท้ายสระ) was the King of Ayutthaya from 1709 to 1732 and the third ruler of the Ban Phlu Luang Dynasty.

King Thai Sa was born Prince Surindra (Thai: พระสุรินทรกุมาร) to King Suriyendra and his principal queen. After the death of his father in 1709 Prince Surindra was crowned as King of Siam and took the reigning name Bhumindaraja (Thai: พระภูมินทราชา). He appointed his brother Prince Voraraj as the Front Palace. The king was said to be very fond of silver barb that he forbade anyone but himself from fishing them or else they would be fined. This earned him the epithet King of the Backyard Pond or King Thai Sa.

His reign was marked by the building of many canals, and "large sea-going vessels". Siam also exported many live elephants.

In 1715, Nguyễn Phúc Chu the Nguyen lord who supported King Keao Fa III invaded Oudong and King Thommaracha III and Prince Ang Tong along with their families fled to Ayutthaya. King Tai Sa ordered Chao Phraya Chakri to invade Cambodia to restore King Thommarcha in 1717. The Siamese fleets suffered defeat by the Vietnamese at Banteay Mas yet on the land the Siamese were able to reach Oudong in 1718 and eliminated Vietnamese troops in the city. King Keao Fa, however, took negotiating measures and agreed to pay tribute to the Siamese court.

King Thai Sa had three sons - Prince Naren, Prince Abhai and Prince Paramet. In 1732, while King Thai Sa was on his deathbed he gave the throne to Prince Abhai since Prince Naren, his elder brother had entered the priesthood. The two remaining princes rose in armed rebellion against their uncle. Prince Phon, the younger son of Suriyenthrathibodi managed to defeat his nephews and took the throne as King Borommakot.