The First King, or the 145th King, also simply referred as King Fritz and later as King Reiss, was the first King of the Wall nation and the 145th King of Eldia, before Marley took back the contintnet. He was an unnamed Titan Shifter who was said to have brought peace for the Eldians who abandoned the mainland. But this peace came at a price, as most of humanity's memories were erased in the process. He was born as a Fritz of the royal family and later he made his new kingdom and changed his name with Reiss, while the other Fritz members that had not fled with the others remained in the continent of Eldia and lost to Marley during the Great Titan War. The royal Eldian family became split in two and the last member of the side from the contintent was Dina Fritz, while the current only living member of the side from Paradis is Historia Reiss.
Over 100 years ago, Humanity was at the brink of destruction. A Shifter known as the First King emerged, with the mysterious power of Coordination. Instead of destroying the Titans, the First King dreamed of a world in which mankind was ruled by them. He created the Walls, then created the Reiss Bloodline of Kings. The First King then eliminated anyone's knowledge of these events, in the hope of creating his perfect utopia.
The only people immune to his mental manipulation were the Ackermans the the Asian Clans. This lead to centuries of persecution to both groups, as both were nearly on the brink of extinction.