The character in Pippin are based very loosely on historical figures from medieval Western Europe. Pippin is modeled after a Prince Pepin, son of King Charlemagne. Charlemagne’s mother, Bertrada (or “Berthe Greatfoot”) is also in the show. In 806 A.D., Charlemange divided his kingdom among three sons: Pepin (Carloman), Charles, and Louis. Both Pepin (king of Italy) and younger brother Charles (king of Neustria) died prematurely (respectively in 810 and 811 A.D.). Only Louis “the Pious” remained alive – in the show, this is “Lewis”, the narcissist.
 Charlemagne |
That’s the short version – in reality though, Charlemagne actually had two sons named Pepin, and the Pippin of the show is a mixture of the two.
The first son was known as “Pepin the Hunchback”, and his mother was Himiltrude, a 13-year-old daughter of the Lombard king. Bertrada arrange the marriage against Charlemagne’s wishes. After taking over the Lombard kingdom, Charlemagne annulled the marriage, making his first son illegitimate. In 792, he became the centre of a plot to overthrow Charlemagne and his three other sons, but the conspirators were found out, and Pepin was sent to a monastery where he spent the rest of his life.
The second Pepin was originally named “Carloman”, but this was changed to Pepin, likely to ensure that he fully replaced the original, now illegitimate heir. He was educated and groomed to be ruler of Italy and eventually heir to the Holy Roman Empire. Pepin had a son and five daughters, but died before his father, and so the kingdom passed to his brother Louis.