Einhard worked as an advisor for Louis the Pious after working for Charlemage 

Einhard quickly became a trusted scholar, advisor, and friend to King Charlemagne. He accompanied the King on all of his travels, including to Rome where he was crowned. Charlemagne trusted Einhard with overseeing construction of several important buildings and as a diplomat. He became a secretary to Louis the Pious, Charlemagne's son, when he took throne after his father's death. He continued to perform diplomatic duties and tutor Louis's sons.