Maha Thammaracha, Maha Thammarachathirat, or Sanphet I, formerly known as Khun Phirenthorathep, was a king of Ayutthaya Kingdom from the Sukhothai dynasty, ruling from 1569 to 1590. As a powerful Sukhothai noble, Phirenthorathep gradually rose to power. After playing many political turns, he was eventually crowned as the King of Siam.

The Ayutthaya Kingdom or the Empire of Ayutthaya was a Mon and later Siamese kingdom that existed in Southeast Asia from 1351 to 1767, centered around the city of Ayutthaya, in Siam, or present-day Thailand. European travellers in the early 16th century called Ayutthaya one of the three great powers of Asia. The Ayutthaya Kingdom is considered to be the precursor of modern Thailand, and its developments are an important part of the history of Thailand.