On the US website of the Royal Thai Consulate-General, Chicago is a document about the two most important Thai Kings, King Rama V (on the left) and King Rama IX (on the right). The document refers to them as the difference makers. I think this two page history is a good one to read. Both of these kings are verrrrry popular with the Thai people and you will see their photos often, in restaurants and elsewhere. We will point out some of these while you are in Thailand, so you will come to recognize their images. Wikipedia also has pages for King Rama V and King Rama IX. We bought a set of fine china in Thailand that is from the period of King Rama V, so you'll be able to see that when we are at the family home in Mae Moh. Originally this style of china was first produced in Thailand during the reign of King Rama V and it was only available to the royalty and his aristocracy, but later King Rama V gave permission for it to be obtained by anyone who had the means to purchase it.
The images of the kings are from the Royal Thai Embassy website in Chennai, India.