Ludwig der Listige is a ruler in the High Middle Ages and Late Middle Ages. Although he only has one province on the High Middle Ages continent map (Moravaria), he controls two provinces on the Late Middle Ages bonus continent map (Ashcrook and Queenshope), making him the only person to have more bonus provinces than regular provinces. He is one of the sons of a powerful yet deceased king, and he fights for the land with his brothers, Lothair III, Karl der Krumme and Childerich IV.
High Middle Ages
In the High Middle Ages Story Questline, he seems to be loyal and helpful, and sends you presents to aid you. However, after you defeat the other brothers he betrays you by either pretending to invite you to Moravaria and celebrate with him yet attempting to assassinate you in the process or sending assassins directly to your city (Ludwig's Treason/Ludwig's War). Eventually though, you defeat him by taking control of Moravia, but he escapes.
Late Middle Ages
He reappears in the Late Middle Ages Bonus Questline and is allied with Kaiserin Konstanze, Freifrau Hagazussa and King Godefrey Darkblood. Princess Myciena is informed that Ludwig had tried to assassinate you and tells you to be careful. Ludwig now says he has changed and doesn't want to cause any more bloodshed over the "little misunderstanding" as you are given the choice to acquire his sectors by force or negotiation.
If you trusted him, he would send you gifts and deceive Myciena into thinking he has actually changed, and then take her hostage and you would have to pay a ransom to free her. If you didn't trust him and fought his territory, you would have set up more defenses in your city to prevent any of his tricks. Nevertheless, he still manages to capture Myciena, but instead of paying his ransom, you instead send your soldiers and bring her back. Afterwards he is defeated again and captured. You can choose to execute him, but he wouldn't cause any more trouble even if you don't and lives the rest of his life in your prison (supposedly).
His name translates to "Ludwig the Cunning" in German, foreshadowing his true nature.
The Story of the four brothers reflects actual history and custom under the Frankish Empire. Charlemagne had one son when he died, so his son became Emperor of all the lands of the Franks this was all of Austria, Belgium, Luxembourg, Netherlands, Slovenia, Switzerland & France (except Brittany), Spain north of the Ebro, Italy as far south as Rome (except Venice), Germany to the West of the Elbe, However Charlemagnes Son had 3 sons when he died and the lands were split between them.