This artwork is one of the scenes of the fighting between Intharachit and Hanuman in Ramakien.
Ramakien is the classic literally of Southeast Asia, which influenced by the Ramayana of India.
Intharachit is the Giant who is the second most powerful adversary also the son of Thotakan, king of Demon, who is the enemies of Phra Ram, The powerful most high on earth
Hanuman is the God-king of Ape, who supported Pha Ram and act as Monkey