When a Siamese King is officially crowned, he normally pledges his first royal command known as ‘Phra Phathom Borom Ratcha Ong-kan’. Although the royal command is mainly given for a ceremonial purposes, to some extent it indicates the status of kingship, the interrelation between kingship and law, the relationship between state, ownership and individuals, and the evolution of the state and political system. From around 2005, Thailand's politics has seen considerable conflict, and ‘Phra Phathom Borom Ratcha Ong-kan’ has broadly been cited to justify the status and righteousness of Thai monarchy. However, there has been little academic attention to the symbolic meanings and historical development of this first royal command. Moreover, most studies on kingship tend to focus on the ‘Dhammaraja doctrine’, which underpins the royal command but often neglect its historical layers and dynamic contexts. This chapter will examine the historical development, significance, and relevance of the concept ‘Phra Phathom Borom Ratcha Ong-kan’. The chapter will start by exploring the origin and importance of coronation ceremony and the first royal command. This will be followed by discussion of the development of the first royal command from the Ayutthaya to Rattanakosin kingdoms, mainly from the founder of Bangkok to the ninth reign of the Chakri Dynasty. Some critical analysis of the adjustments of words and phrases in the royal commands throughout history with regard to kingship, legal concepts, and the relation between state, ownership and individuals, particularly from the age of westernisation and reformation from the reigns of King Mongkut onwards, will also be provided. In the final part, it will critique controversies and contemporary context of the first royal command.