|Frieda's Titan was superior to all other Titans. You could say her Titan had unsurpassable power.|
|— Rod Reiss claims the Founding Titan is the strongest Titan|
The Founding Titan (始祖の巨人 Shiso no Kyojin?) is one of the Nine Titans that was once in the possession of the Reiss family, who passed it down from generation to generation. Its screams can alter the minds of both humans and Titans, but in the case of the former, some bloodlines are exempt from its power. It is currently in the possession of Eren Jaeger, although Eren's lack of royal blood means the Titan is unusable in its current form.
The Founding Titan's power is used by screaming. Whoever has the Founding Titan does not have to transform in order to use its abilities, and the screams of a human would suffice. Furthermore, the screams do not have to be loud or even "screams": Frieda Reiss was able use the memory alteration ability by casually talking, although her target was only Historia who was right in front her.
The Founding Titan enables its wielder to control the Titans by screaming. It has been observed that Pure Titans simply obeyed the orders given by its wielder while Intelligent Titans can sense its use, though they are seemingly not influenced by its control. It is similar to the Female Titan's ability to attract Titans by screaming.
The Founding Titan's screams also affect humans, but not every human is affected by this ability. The King once used this ability to make humanity inside the Walls forget about the past, except a few minority bloodlines. Frieda used this ability to make Historia forget about her, but these memories resurfaced when Historia touched Eren Jaeger, who currently possesses the Founding Titan.
Supposedly, the Founding Titan's power can only be used by a member of the Reiss family. However, Eren Jaeger used its ability once before, so it is speculated that it is possible to use its abilities without having Reiss blood.
Vow renouncing war
Members of the Reiss family that inherit the Founding Titan are taken over by the First King's vow renouncing war (不戦の契り Fusen no chigiri?). Even though the Founding Titan can control other Titans and potentially wipe them all out, no Founding Titan from the Reiss family bothered to do it. As children, Uri Reiss pleaded alongside Rod to their father to free humanity from the Titans, but their father refused. After Uri inherited the Founding Titan himself, his mindeset changed, and did nothing as the previous holders had as well. The First King thought that true peace can be achieved by allowing humanity to be ruled by, and living in constant fear of, the Titans lurking outside the Walls.
The Founding Titan's power was used to build the Walls. The Reiss family used the Founding Titan's power to alter the memories of humanity inside the Walls so they can be controlled. The First Reiss King made everyone inside the Walls forget about the past. The Ackermann family and the Oriental clan were unaffected by this power and turned against the King's ideology. Fearing the inability to control them, the King prosecuted both bloodlines to near extinction.
After the Fall of Wall Maria, Grisha Jaeger goes to the Underground Chapel where the Reiss family is and transforms into a Titan. Frieda Reiss also transforms and battles Grisha, but loses and is eaten. Grisha obtains the Founding Titan and then proceeds to kill every single member of the Reiss family, except Rod Reiss who escapes. He later finds his son Eren and injects him with an unknown serum, turning his son into a Pure Titan. Eren eats Grisha and inherits the Founding Titan.
Before fleeing the Scouts in the Forest of Giant Trees, Reiner states that the connections between the Reiss family and the Order of the Walls make Historia Reiss a valuable asset for the Warriors' mission, and having her with them will make their goal much easier if Eren Jaeger is not the "Coordinate" they are searching for.
Later that day, the Warriors' suspicions are confirmed when Eren unleashes the Founding Titan, striking the hand of a smiling Titan, screams, and causing all the surrounding Titans to swarm it and tear it to pieces. When Reiner and Bertholdt approach him afterward, Eren's outburst towards them once again triggers the Founding Titan and sends the nearby Titans rushing towards the Warriors, allowing for the Scouts to escape. On the journey back to Wall Rose, all Titans previously encountered ignore the Scouts and instead run in the Warriors' direction under Eren's subconscious orders.
A squadron from the Military Police led by Kenny Ackermann kidnaps Eren Jaeger and Historia Reiss and brings them to Historia's father, Rod Reiss. After reading a note from Eren on how Ymir got her Titan powers, Hange Zoë theorizes that the government is planning to devour Eren to gain his power.
Eren awakes, chained up and gagged, in the Reiss family's Underground Chapel, the location where the power has been passed down for generations. As he slowly wakes up, he has a vision of Frieda Reiss, a former Founding Titan, bushing her hair.
Later, Rod and Historia Reiss touch Eren's back, triggering a chain of memories: Eren unlocks memories of his father, fighting Frieda and eating her (inheriting the Founding Titan), slaughtering the Reiss family, and then feeding himself to Eren. Historia unlocks memories of Frieda who once used the Founding Titan's power to erase herself from Historia's memories.
- Frieda Reiss normally had blue eyes, but when she transformed into an Intelligent Titan, her eyes glowed purple. When Grisha Jaeger devoured her and obtained the Founding Titan, his normally green eyes turned purple as well.
- The Founding Titan's power is extremely similar to the Beast Titan's ability to control Titans, which he also uses by screaming or talking.
- The songs Guren no Zahyou and ERENthe標 both reference the Coordinate in their titles, and Guren no Zahyou also mentions it in it's lyrics.