The Reiss family is the current royal family of Eldia that descended from Karl Fritz, the First King of the Walls. They branched off from the original royal family after the Great Titan War, masqueraded as a minor noble family living inside northern Wall Sina, and set up a false King and royal family to further draw attention away from themselves. They passed the Founding Titan between ruling monarchs every 13 years, until it was stolen by Grisha Jaeger in the year 845. Currently, Historia Reiss, the illegitimate daughter of the late Rod Reiss, is the queen.
History: In ancient times the royal family was known as the Fritz family. Around 2,000 years ago, the leader of a tribe known as the Eldians would have children with Ymir Fritz as a "reward" for being the first to gain the power of the Titans and bringing prosperity to the tribe. Their descendants would go on to build the nation of Eldia.
Story: During the day of fall of Wall Maria in 845, the Reiss family goes to the village chapel to pray. However, Grisha Jaeger, a man with the power of the Attack Titan invades the chapel and meets them there. He begs Frieda Reiss to save the people inside the Walls from the Titans, but she refuses.
Source: Reiss family (Anime), available under CC BY-SA 3.0.