Zhu Bajie is one of Xuanzang's disciples. In the story, Zhu Bajie used to be an important Naval Commander in the River of Heaven. As Marshall Tien Peng of the Heavenly Canopy, Zhu Bajie commanded 100, 000 naval soldiers. However, his flirtation with the Moon Goddess, Chang E, at the Peach Banquet, causes Zhu Bajie to be banished to the mortal world to be reborn as a human being. However, due to an error in the Wheel of Reincarnation, Bajie became a loathsome half-man and pig creature on earth. According to the Tathagata, Zhu Bajie's great love for sensual indulgence also causes him to sin in the Cloud Pathway Cave in the Mount of Blessing. Eventually, Zhu Bajie is converted to the great Buddhist faith and guards XuanZang on his journey to bring back the Buddhist holy scriptures from the Blessed Region of the Buddha to the people of China.
After performing his part in the Journey To The West, Zhu Bajie is given the title of Altar Cleanser by the Tathagata.
Zhu Bajie is not entirely happy with this new title/role because both Tripitaka (XuanZang) and Sun Wukong (Monkey) have been made Buddhas. The Tathagata replies that he has only given the above title and position to Zhu Bajie because of his voracious appetite, his laziness, and his less than stellar physical profile. The Tathagata notes that Zhu Bajie's heart is still unregenerate and that he has not purged himself from his lusts. Thus, he cannot be made a Buddha.
Although his new position seems like a lesser honor (compared to that given to Sun Wukong and Xuan Zang), the Tathagata reminds Zhu Bajie that his new job of cleaning the altars after all the Buddhist services will accord him plenty to eat. So, this new job is really a reward for Zhu Bajie because he can continue to indulge his great love for food.