- Directors: Tony Jaa, Panna Rittikrai
- Producers: Prachya Pinkaew, Tony Jaa, Panna Rittikrai, Akarapol Techaratanaprasert
- Writers: Screenplay, Ek Iemchuen, Nonthakorn Thaweesuk, Story, Tony Jaa, Panna Rittikrai
- Genres: Action
- Actors: Tony Jaa
The film begins in the year 1974 of the Buddhist calendar (which corresponds to 1421 in the Gregorian calendar), in feudal Thailand. It is a time of political upheaval, treachery and danger. The opening scene explains how during the reign of Boromarajatiraj II of the Ayutthaya Kingdom, the Ayuthaya royal court became more powerful then the Sukhothai kingdom and expanded to the east. The Ayuthaya army sieged the Kingdom of Gods for several months. The king sent his son, Prince Indraracha to rule the kingdom. At the new kingdom, Lord Sihadecho is a provincial ruler, and a gallant and noble warrior of a formally great dynasty. His son, Tien, a spirited and unyielding youth, aspires to be just like his father, but is forced to undergo dance lessons instead much to his disdain. Meanwhile, the treacherous and power-craving Lord Rajasena, a former city administrator of the capital city, plots to seize total control of all Asia and has amassed the greatest army in Asia. Rajasena sends out vicious assassins to murder Lord Sihadecho’s family and his loyal soldiers. The only survivor from this massacre is Tien, who manages to escape with deep vengeance in his heart, and becomes a wild and feral child.
The film ends on a cliffhanger with Tien, after defeating hundreds of Rajasena’s warriors, being finally overwhelmed by hundreds more. Rajasena orders Tien to be taken away to be slowly tortured to death. It is unclear whether Tien survives, and if he does, how it is so. An extremely ambiguous and vague voice-over explains that Tien “may find a way to cheat death again”, and Tien is shown with a fully-grown beard (which he doesn’t have in the film) standing in front of a scarred golden Buddha statue, perhaps indicating reincarnation,some say Tien is Ong Bak himself or some other mystical solution. Nevertheless, the story is set to be resolved and continued in the sequel Ong Bak 3.