King Ramkhamhaeng, a son of King Sri-inthrathit, is the most famous and dynamic monarch ever to rule the Sukhothai kingdom. He was a valiant warrior, a wise statesman, a far-sighted scholar and a brilliant diplomat. His attributes of a warrior can be seen from the fact that during his reign, the Sukhothai was an extensive kingdom, bordering in the north on the kingdom of Lannatai at Lampang, including in the north-east Phrae, Nan and Luang Prabang and in the east Wiengchan (Vientiane). To the south, it extended to the towns in the Malay Peninsula and in the west to Tenesserim, Tovoy, Martaban and Hangsawadi up to the Bay of Bengal. 

King Ramkamhaeng was an absolute monarch who organized the government of the country along military lines. He was himself the head of the army and all the governors and officials in the cities and towns served under him, in diminishing ranks. He also governed with justice and magnanimity his own people as well as people of other nationalities that lived within his kingdom. Their welfare received his unfailing attention. He was accessible to his people. For example, he had a bell hung in front of a palace gate so that any subject with a grievance could ring it and ask for justice. He also showed considerable interest in the moral education of the people. He persuaded them to observe the simple Buddhist precepts, to make merit and give alms, and to attend a sermon regularly.

King Ramkamhaeng created in 1283 the first Thai alphabet so that it was a symbol of the nation's independence. Although his original script has undergone some changes, it is still in use now. It consists of 44 consonants, 32 vowels, and 5 tones of sound. In 1292, King Ramkamhaeng had a stone inscription built. It is considered to be a seminal source of Sukhothai history as well as a masterpiece of Thai literature. The Thais still learn about Sukhothai in the 13th century from this inscription.

King Ramkhamhaeng was a paternalistic and benevolent king. His people were happy. Most of them engaged in agriculture while others carried on trade, which was greatly facilitated because no tax was collected. This style of kingship has caused posterity to regard the Sukhothai Kingdom's heyday as a 'golden age" in Thai history. Under the reign of King Ramkhamhaeng, Sukhothai was both prosperous and well governed.