Ok or Ouk Chatrang is Cambodian Chess, Chess played in Cambodia and Makruk is Thai or Siamese Chess, Chess played in Thailand (old name was Siam).
The very first account of Siamese Chess is due to La Loubère, the ambassador of French King Louis XIV to the Kingdom of Siam in 1687-8. More will be given by the Captain James Low to Asiatic Researches in 1836 and, finally, Edward Falkener will supply reliable information he had got from Prince Devawongsee, Minister of Foreign Affairs of H.M. the King of Siam, in 1889.
Ouk Chatrang is most probably played in Cambodia for a long time, as it is depicted in several reliefs found on the Angkor temples which date from the XIIth century.
In the 1st millennium AD, the Indian culture spreads into south-east Asia. Under the influence of Tamil spice traders coming from the South of India and Ceylon, especially under the Chola dynasty, several indianised kingdoms were founded like Srivijaya in Sumatra and Java, Champa in South Vietnam, Zhenla and other Khmer states in Cambodia, etc. Magnificent temples in Borobudur (Java) or Angkor (Cambodia) are still there to remember. Indians brought Hinduism, Buddhism, Sanskrit and writing alphabets, and also Chaturanga: Chess.
The first kingdoms founded by the Khmer people, Funan, Zhenla, felt under Javan domination circa 700. Jayavarman II, a prince educated in Java founded the Angkor Khmer kingdom in 802. Then, it can be assumed that Chess came in Cambodia from Java which in turn held it from South-East Indians.
There are several points which merit a discussion:
The bulky shape of the piece is apparently an old tradition since it can be seen on Angkor temples. Only the Horse has a recognizable form. A similar design is found on the set of Malay Chess shown in Murray’s History of Chess. That reinforce the link between Cambodia and Malay/Java.
A Boat is used in place of the Rook. This is known to be common in India as well, especially in the South and in the East (Bengal) and also in Java according to Murray. (It is also the case in Russia but we think that the reason is different). Boats are attested for sure in Indian Chess since circa 1500. Replacing the Chariot by a Boat in the warfare for people trading and struggling onto the seas is something which can be easily understood. It reinforces the maritime arrival of Chess in this region.
The sense of Elephant (Bishop) is hidden both in the name and in the form of the piece. In battlefield, in troops parade, noblemen used to sit on the back of elephants. Also, one can say that elephants are the pillars of the fighting army.
More important is the move associated to this piece: it can step 1 case in the 4 diagonal directions as well as straight forward. This move was already attested by the Persian al-Beruni in India, his account of his trip in that country circa 1030. He said that these 5 directions were to remind the four feet and the trunk of the animal ! The original Elephant move which consisted in a diagonal leap on the 2nd square allowed to reach only 1/8 of the board. This genital weakness received several attentions in different regions in the world : the Korean gave their Elephant an elongated Knight move (see Changgi), the European invented our modern Bishop sometimes at the end of the Middle Ages. This 5-limb stepping, probably born in Buddhist centers according to H.J.R. Murray, is a third response.
The Pawns are in an advanced position, on the 3rd line. This was probably adopted to accelerate the original game which was slow. Again, it can be compared to other solutions made in other places like the Arab Ta’biyat in Shatranj or the initial phase (werera) in the Ethiopian Senterej.
The Pawns are either flat tokens or cowrie shell (having a slot on one face). They get their promotion when reaching the 6th row (the 3rd from the opponent’s edge). Then, they are turned upside down to show that promotion.
The last 4 points can also be found in Shogi, the Japanese Chess. Modern Shogi historians now believe that Shogi has been influenced by Chess played in the South-East regions. There were frequented commercial maritime routes connecting Japan to India through the Malay Straits in these times.