Prasat Thong Somdet Phrachao Prasatthong ( ) ( reigned 1629 – 1656 ) was the first king of the Prasat Thong dynasty , the 4th dynasty of the Siamese Ayutthaya kingdom . Accounts vary on the origin of Prasat Thong . While traditional Thai historians hold that he was an illegitimate son of King Ekathotsarot , Jeremias van Vliet ' s account states that he was the maternal cousin of King Songtham – his father was " Okya " Sri Thammathirat ( ) , elder brother of the mother of King Songtham . He was born during the reign of King Naresuan around 1600 and was known to cause mischief in the royal court . He ruined the palace Agricultural Initiation Ceremony and was threatened with execution ; only pleas from the queen of King Naresuan won a reduction of the punishment to life imprisonment . He was later pardoned and given the title of " Okya " Sri Vorawong ( ) – a high ranking title of royal page . Rise to power . The rise of Prasat Thong to power was documented in van Vliet ’ s " The Historical Account of the war of Succession following the death of King Pra Interajatsia " ( 1650 ) . As the king ' s maternal cousin , he held great influence . It is said that he was a very ambitious prince and wanted to become a king . King Songtham had had his brother Prince Sri Sin as the Front Palace , technically his successor , but a palace faction including Prasat Thong persuaded the king to give the throne instead to his son Prince Chetthathirat . When King Songtham died in 1628 , Chetthathirat ascended the throne and a great purge of the mandarins who had supported Prince Sri Sin was instigated , including the " Samuha Kalahom " or Defence Minister . Prasat Thong then replaced him as the Defence Minister with the new title of " Okya " Suriyawong ( ) . Prasat Thong had Yamada Nagamasa , the head of Japanese mercenaries then known as " Okya " Senaphimok ( ) , as a supporter . Prince Sri Sin escaped into monkhood to save his life . However , he was lured into the palace with his monastic robes off and with princely attire . He was arrested and then exiled to Phetchaburi where he was thrown into a well to be starved to death . The prince was narrowly saved by the local monks who thrown a body into the well as substitute . Prince Sri Sin then organized a rebellion in Petchaburi . Prasat Thong sent " Okya " Kamhaeng and Yamada Nagamasa to lead the Japanese troops to crush down the rebels . Prince Sri Sin was captured and executed in Ayutthaya . With the Prince Sri Sin gone , Prasat Thong was in full power . In 1629 , his father died . The funeral was held in grandeur and his father ’ s ashes were cremated twice – a practice reserved for royalty . On that day King Chetthathirat called for an audience with all the nobles but all of them had gone to the funeral – much to the king ’ s great anger . The king threatened to punish Prasat Thong but " Okya " Phraklang ( the Minister of Trade who was Prasat Thong ' s ally ) managed to calm the king and convince him of " OkyPrasat Thong ' s " innocence . The king was unprepared when Prasat Thong hurled armies into the palace . The king fled but was captured and executed . Prasat Thong installed the king ’ s brother – the eleven - year - old Prince Athittayawong – as the new puppet king with Prasat Thong as the regent who crowned himself as the second king . Prasat Thong strived to eliminate his allies - turned - rivals – the " Okya " Kamhaeng who contested him for the throne and Yamada Nagamasa who objected to the takeover of the throne by Prasat Thong . He quickly condemned " Okya " Kamhaeng to treason and execution followed . And he sent " Okya " Senaphimok south as the governor of Ligor , away from Ayutthaya . As long as the Japanese mandarin leave the city , only about a month after his ascension , the child - king was deposed and was subsequently executed . " Okya " Suriyawong crowned himself as the full - fledge King of Siam . Upon arriving Ligor , " Okya " Seniphimok heard of the coup at Ayutthaya and rebelled . However , he was poisoned to death through his wounds by an agent sent by the new king . Reign . As a powerful and decisive leader , he promulgated many criminal laws and sometimes , according to Van Vliet , he even executed prisoners by himself . Siam was a major trading center attracting Europeans merchants . Prasat Thong was interested in controlling the towns in the southern peninsular , perhaps , because of profits from oversea trade . Ayutthaya lost northern subjugated principalities such as Chiangmai . His son , Narai , eventually began a significant relationship with European countries .