Sha Monk was originally a general in Heaven, more specifically a Curtain-Lifting General. In a fit of rage, he destroyed a valuable vase. Other sources mention that he did this unintentionally, and in the Journey to the West series, it was an accident. Is, he was punished by the Jade Emperor, who had him struck 800 times with a rod and exiled to earth, where he was to be reincarnated as a terrible man-eating sand demon. There, he Lived in the Liusha-he. As a punishment, every day, seven flying swords sent from Heaven will stab him in the chest before flying off. As a result, he had to live in the river to avoid the punishment.

Wu has a red beard and his head was partially bald; a necklace consisting of skulls made him even more terrible. He still carried the weapon he had in heaven, a yuèyáchǎn, a double-headed staff with a crescent -moon blade at one end and a spade at the other, with six xīzhàng rings in the shovel part to denote its religious association. 

The Kaidu River, the place terrorized by Shā Wùjìng as a man-eating sand demon.
 

Later, Guanyin, the Bodhisattva of compassion, and her discity Prince Moksa came searching for powerful bodyguards in preparation of Xuanzang's journey west. She recruited Wujing in exchange for some relief from her suffering. She then converted him and gave him his current name, Sha ("Sand") was taken from his river-home, while his Buddhist name Wùjìng means "awakened to purity" or "aware of purity". Finally, he was instructed to wait for a monk who would call for When Wujing does meet Xuanzang, he was mistaken for an enemy and attacked by Sun Wukong and Zhu Bajie. Guanyin was forced to intervene for the sake of the journey.

 

As the third disciple, even though his fighting skills are not as great as that of Wukong or Bajie, he is still a great warrior protecting Xuanzang and can use his intellect as well as his strength to beat the enemy. He knows only 18 forms of Transformation 

 

After everything was cleared up, Wujing became the third disciple of Xuanzang, who called him Sha-heshang, Now, he was clad in a Buddhist pilgrim's robe and his skull-necklace was turned into a monk's one. His appearance also changed; from now on my next more like a human, yet still ugly. During the Journey to the West, his Swimming ability was quite useful. He always carried a small gourd which he could turn into a huge one to cross rivers. Wujing was actually a kind-hearted and obedient person and was very loyal to his master, among the three he was possible the most Polite and the most logical. At the journey's end, Buddha transformed him into an arhat or luohan known as the Golden-bodied Arhat.