Ong Boun

{{Infobox monarch

| name =Phrachao Siribounyasan
{{lang|lo|ພຣະເຈົ້າສິຣິບຸນຍະສານ}}

| title =King of Vientiane

| succession = King of Vientiane

| image =

| caption =

| reign = 1767–1781

| coronation =

| full name = Somdet Brhat Chao Dharma Adi Varman Maha Sri Bunyasena Jaya Setha Adiraja Chandrapuri Sri Sadhana Kanayudha

| predecessor = Ong Long

| successor = Nanthasen

| spouse =

| issue =

| royal house =

| dynasty =

| father = Setthathirath II

| mother =

| birth_date =?

| birth_place =Vientiane, Lan Xang

| death_date = November 1781

| death_place =Vientiane

| date of burial =

| place of burial =

|}}

Phrachao Siribounyasan ({{langx|lo|ພຣະເຈົ້າສິຣິບຸນຍະສາຣ}}; {{langx|th|พระเจ้าสิริบุญสาร}}; died November 1781), also known as Ong Boun ({{lang|lo|ອົງບຸນ}}), Bunsan or Xaiya Setthathirath III,{{cite book|url=https://books.google.com/books?id=Ncqj2QWkFQMC&dq=Chao+Inthavong&pg=PA125|title=The Kingdoms of Laos: Six Hundred Years of History |author=Peter Simms |author2=Sanda Simms |year=2001 |publisher=Psychology Press |isbn=978-0-7007-1531-2 }} was the 3rd king of the Kingdom of Vientiane (r. 1767 to 1781).

Ong Boun was the second son of Setthathirath II. He was appointed the governor of Xiangkhouang in 1735. In 1767, his elder brother Ong Long died without heir. With the help of Phra Vo, Ong Boun crowned the new Vientiane king.{{cn|date=August 2020}}

At that time, Vientiane was a vassal state of Burma.{{cite book | last=Tarling | first=Nicholas | title=The Cambridge history of South East Asia: From c. 1500 to c. 1800 | year=1999 | volume=1 | number=2 | page=238 | publisher=Cambridge University Press | isbn=978-0-521-66370-0}} The Burmese King considered Lao kingdoms as his base to expand further east. So, King Taksin of Siam decided to invade Lao kingdoms. In 1778, a Siamese army under Somdej Chao Phya Mahakasatsuek (later Rama I) invaded Vientiane.Wood, p. 268 After a siege of four months, the capital was captured by Siam.Wyatt, p. 143

Ong Boun fled into jungle, finally, he decided to submit to the Siamese. Since then, Vientiane became Siamese dependency. Most of his children were taken to Thonburi as hostages, including Nanthasen, Inthavong, Anouvong and Khamwaen. Khamwaen later became a concubine of Rama I.คึกฤทธิ์ ปราโมช, ม.ร.ว.. โครงกระดูกในตู้. กรุงเทพฯ : สำนักพิมพ์สยามรัฐ, พิมพ์ครั้งที่ 8 พ.ศ. 2547.

However, Ong Boun revolted against Siam in 1780, he killed the Siamese appointed governor Phraya Supho. In November 1781, he was captured by Siamese, and executed.