The early Chinese ruler you are referring to is likely the Tang Dynasty, which lasted from 618 to 907 AD. After the collapse of the Sui Dynasty, the Tang unified various kingdoms and established a significant period of prosperity and cultural flourishing, often referred to as a Golden Age.
The reference to the Mongol invasion pertains to a later period, specifically during the Yuan Dynasty, which was established by Genghis Khan's descendants in the 13th century. If you meant to refer to the era that extended beyond the Tang Dynasty, you might also be considering the Song Dynasty (960-1279), which followed the Tang and experienced its own Golden Age before being conquered by the Mongols.
If you need further clarification or details about a specific dynasty or period, feel free to ask!