Shenlong Xing Zhu Ep 21

Gu Zhengfeng was originally the divine dragon that guarded the Dragon Star. He was seriously injured in an ancient battle with alien enemies and fell into a long sleep. He wakes up and finds that the Dragon Star has changed, and is now called evil. In order to investigate and retrieve the treasure hidden in the Dragon King Academy, he changed into a human form and entered as a tutor in the Dragon Slaying Department.(Source: TVDB)