(This is one version of the Khmer foundation-legend; what they all have in common is the idea that the Khmer people spring from the union of a prince from India and a native naga princess).
In India once there lived a prince, Preah Thong by name, who was told in a dream to take a ship and sail to a golden land in the east where he would establish a great kingdom. After many days sailing the prince came upon a beautiful and uninhabited island. Preah Thong named it Nokor Kok Tlok, Kingdom of the Tlok Tree, after a large tlok tree by the shore. Possibly feeling he had done enough for one day Preah Thong fell asleep under the tlok tree, and when he awoke it was night. The moon was full and he gazed on the sea, wondering about his new kingdom, and especially about the lack of people, and as he watched he saw human figures emerge from beneath the waves.
The prince watched from behind the tree as the beings spread a feast under the trees. The men fell to sporting with wrestling and sword-play on the sand, while the women strummed musical instruments and sang sweet songs. All were comely, but in their midst was a lady more beautiful than any. Overcome by her beauty, Preah Thong stepped out from his hiding place and introduced himself, asking the lady who she was, and how it came to be that she and her people lived beneath the waters.
The lady permitted him to know that she was Neang Neak (Lady Naga), the daughter of the naga king, that this was the land of the nagas, and that she and her court visited the beach every full moon night for their pleasure. She informed him also that it was a serious breach to speak to royalty before being spoken to, and that he had broken this rule, but as she could see he was a stranger and ignorant of naga etiquette she would permit him to inform her of his name and family before ordering his execution.
Quickly Preah Thong told Neang Neak of his foreign origins and princely station and declared his love, and after further gentle words the princess agreed to take him to the underwater kingdom of the nagas so that he could ask her father for her hand in marriage.
And so Neang Neak took Preah Thong to the kingdom of the nagas, the prince holding her scarf. For three days they celebrated their wedding, and at the end of that time the naga king swallowed the water that had covered the land and Preah Thong and Neang Neak ruled together over the Khmers.
Photo from a site called Shane and Ravy: Our Wedding.
This legend provides the basis for Khmer weddings – the groom, dressed as a prince, holds the scarf of the bride as she leads him to the wedding chamber. In another version of the legend the Indian prince is a Brahmin named Kaundinya and the naga princess is named Soma. The plot is very similar to the story of Preah Thong and Neang Neak except that the island is apparently upstream in the Mekong, and Kaundinya defeats Soma in battle before she agrees to marry him. In yet another version the prince was called Kambu, from which comes the name Kambuja, Cambodia.