[1][2] He was the son of Maha Thammaracha II and great-great grandson of King Ram Khamhaeng the Great.
His mother, who called herself "Saṃtec Braḥ Rājadebī Srī Cuḷālakṣana Arrgarājamahesī Debadhòranī Tilakaratana" (Asokārāma stone inscription) or "Saṃtec Braḥ Rājajananī Srī Dharmarājamātā Mahātilakaraṭana Rājanārtha" (stone inscription 46), was the daughter of King Li Thai (Maha Thammaracha I) and married to her brother, Maha Thammaracha II.Sai Luthai had a full brother, a prince named Asoka, of whom no information is known.
46 describes that the Queen Mother, together with her son "Satṃtec Mahādharrmarājādhipati Śrī Surīyavaṅsa" (Sai Luthai), recaptured Phra Bang (present-day Nakhon Sawan) and Phrae with her army in 762 C.S.
However, after seeing a bad omen, he withdrew, took Yi Kum Kam with him, and left him one of his provinces (possibly Kamphaeng Phet) as an appanage.
Lan Na was ruled by Yi Kum Kam's younger brother Sam Fang Kaen [de].