Phra Aphai Mani (Thai: พระอภัยมณี) is a 30,000-line epic written by Thailand's best-known poet, Sunthorn Phu. It is also part of Thai folklore and has been adapted into films and comics.
The main protagonists are Prince Aphai Mani, a mermaid, and a female yak or ogress.
Phra Aphai Mani (พระอภัยมณี) and his brother, Sisuwan (ศรีสุวรรณ), are Thai princes. Their father sent them away to study with the hope that they would gain knowledge to help them rule the country. Sisuwan learned to sword fight and Phra Aphai Mani learned to play a magical flute that could put people to sleep or kill them. When they returned home, their father was angered by what they had learned and drove them away.
One day while Aphai's companions were lulled to sleep by the sound of his pipe, a female ogress named Nang Phisua Samut (นางผีเสื้อสมุทร), came and took Aphai away to her cave. She disguised herself as a beautiful maiden and Aphai fell in love with her. They lived together until she bore a son, Sinsamut (สินสมุทร). When Aphai found out that his wife was really an ogress, he fled with his son. He was assisted by a family of mermaids, a father, mother, and daughter. The father and mother were caught and eaten by the ogress. The mermaid daughter took Aphai and Sinsamut to Kokaew Phitsadan (Wonder Island) where a hermit saved them from the ogress. Aphai married the mermaid daughter and they had a son, named Sutsakhon (สุดสาคร).
One day, a ship, carrying King Silarat (ท้าวสิลราช) and Princess Suwwanmali of Phleuk (สุวรรณมาลี), passed Wonder Island. The princess was engaged to marry Prince Usaren (อุศเรน) of Lanka. Aphai and Sinsamut asked to join the ship, but the ogress saw them and became very angry. Nang Phisua Samut attacked them and killed King Silarat. Aphai escaped to the shore, where he played his magic flute and killed the ogress. Afterwards, he met Prince Usaren, who was looking for his fiancée.
Meanwhile, Sinsamut swam with the princess to an island and met Sisuwan and his daughter, Arun Rasami (อรุณรัศมี). Together, they went in search of Phra Aphai. When they found Phra Aphai and Usaren, Princess Suwwanmali refused to leave with Usaren. The two parties fought and Prince Usaren fled to his homeland of Lanka.