"It's surprising how much japanese mythology is slipped in to the anime series - I've also seen the monkey god pop up in all sorts of places (or references to him) and it always makes me smile to see him. Mainly because I have fond memories of the Live-Action TV Series 'Monkey' which deals with the legend of him escorting a holy man across from japan to india." - Spanky

The Monkey King is from the centuries-old story "The Journey to the West" that is very popular in both China and Japan. It's about a monk that is sent from China to India by the Goddess of Mercy (Kanon) to find the sutras with the true teachings of Buddhism and bring them back and enlighten the people of China. He is accompanied by three monster-spirits, the Handsome Monkey King (who was imprisoned by the gods for stealing the peaches of immortality and freed by the monk), a pig spirit, and a water spirit. The journey last for years, and they have all kinds of adventures. The story is REALLY long, but if you like Japanese lit it is worth tracking down. It's also based on a real monk that really did travel to India, but probably not with all the monsters.

The Monkey King is definately the most popular figure in the myth. He's kind of an antihero, ugly, impatient, and rebellious. He fights with a stick that can change sizes on command (like the stick Enma changes into).

This story pops up all of the time in anime. Goku from Dragon Ball is based on the Monkey King, Saikano is a weird retelling of the story. It's in the play they do in Love Hine, one of the bad guys in Shaman King, and one of the villains in the ROD OVA. Anyway, check it out if you like.