The Four Heavenly Kings, Tamon-ten, Jocho-ten, Jikoku-ten, and Komoku-ten, were assigned by the Jade Emperor to guard the heavens from all four directions. Tamon-ten was assigned the north, Jocho-ten the south, Jikoku-ten was directed to guard the eastern gates, and Komoku-ten the western gates.
Each King wields one of the four sacred weapons: Jocho-ten skillfully wields Jian the Thunder Sword. Tamon-ten wields Sanjiegun the Thunder Flail, Jikoku-ten wields Saitsu the Lightning Trident, and Komoku-ten wields Gun the Heavenly Pole, the weapon of the Western Dawn.
If you want to know a little more about the Heavenly Kings, you must visit the Makipedia.