Fa Ngum
Taking advantage of rapid decline in the Khmer Empire, Phra Chao Fa Ngoum ( RTGS "Fa Ngum", cf. ) defeated the Khmer and united the Tai "mueang" of what is now Laos and Isan into the mandala kingdom of Lan Xang in 1354. Fa Ngoum was a grandson of the ruler of Muang Xoua (RTGS "Mueang Sawa"), modern-day Louang Phrabang. Lan Xang was powerful enough to thwart Siamese designs from their base at Sukhothai and later Ayutthaya.