Uthong or Ramathibodi I (1314–1369) was the first king of the kingdom Ayutthaya (now part of Thailand), reigning from 1351 to 1369. He was known as Prince U Thong before he ascended to the throne on March 4, 1351. A native of Chiang Saen (now in Chiang Rai Province) he claimed descent from Khun Borom and propagated Theravada Buddhism as the state religion.