To the Tang Dynasty: Guan Zhenguan

An all-around master of the 21st century traveled through the Tang Dynasty and became the grandson of Prime Minister Du Ruhui. He used modern knowledge to continuously innovate for the Tang Dynasty. During the Zhenguan period, he got an elixir of longevity by mistake. He originally thought it was a fake, but after accidentally eating it, he actually lived forever. In the end, he continued to make the Tang Dynasty stronger and retired. (This story is partly fictional and partly adapted. Please do not take it seriously.)