Karl Fritz (Anime)

First Reiss King was the first ruler of the Walls and possessed the Founding Titan which he used to alter humanity's memory.

Founding Titan
The first king's Titan form had long, straight hair and sharp teeth. In contrast to its thick legs, the upper part of its body was quite skeletal, with its ribs visible through the skin. Its arms were thin and long, similar to those of the Beast Titan.

History
The first king used the power of the Founding Titan to construct three concentric Walls around the last remaining territory of humanity in which mankind could finally live in true peace. With the last remnants of humanity gathered within the Walls, the king used his power again to alter their memories, erasing all knowledge about the world outside the Walls and the history before their creation. However, some bloodlines were excluded, such as the Ackermann family and the Oriental clan. To prevent the risk of these unaffected groups spreading information about the world beyond the Walls, King Reiss offered positions of nobility in Wall Sina to these minority families, and most accepted the offer. However, the Ackerman family and the Asian clan rejected King Reiss's ideology and turned against him. For this reason, King Reiss ordered for these families to be hunted down and exterminated.

Legacy
Throughout the generations, the ideology of King Reiss was carried through the monarchs of the Reiss family, and none would tell of the history of the Eldian Empire before the raising of the Walls.

The Uprising arc
When Eren and Historia Reiss are captured and taken to Rod Reiss, he tells the two the history of the Reiss family and the passing of the First King's ideology through the line of monarchs in the past century, preventing the truth of the world from being known to the people of the Walls.