Tang Priest was sealed by Tathagata. Why the Buddha?

Tang Priest was named Tathagata's merit Buddha. In his previous life, Tang Priest was the second disciple of the Tathagata, who was made of gold. Because of his contempt for Buddhism, he was demoted to the lower bound by the Tathagata. Under the guidance of Guanyin Bodhisattva, he went to Wan Li not far away to seek scriptures at the behest of Emperor Taizong.

On the way, three disciples, the Monkey King, Zhu Bajie and Sha Wujing, went through 81 difficulties and finally got the true scriptures. They returned to the Tang Dynasty, where they made a positive result and were named "Tan Gongde Buddha" by the Tathagata Buddha.

Extended data:

The Tang Priest in The Journey to the West, whose common names are Chen Yi and posthumous title Jiang Liuer, was given the surname Tang by Emperor Taizong. Jin Chan, the elder of reincarnation, is the second disciple of Tathagata. He is a posthumous child. Because of his parents' tragic and bizarre experiences, he grew up in a temple, became a monk in Jinshan Temple, and finally moved to a famous temple in Beijing to practice.

Tang Priest is studious and highly savvy, and stands out among the monks in the temple. Emperor Taizong invited him to hold a "land and water conference" and was elected as a monk by Guanyin Bodhisattva. Became sworn with Emperor Taizong and went to the Western Heaven to learn Buddhist scriptures.