|One thousand, eight hundred and twenty years ago, our ancestor Ymir Fritz made a contract with the Devil of All Earth and obtained the Power of the Titans.|
|— Grisha's father tells his son of Ymir's tale|
The Devil of All Earth (大地の悪魔 Daichi no Akuma?) is a figure of Eldian mythology who made a deal with Ymir Fritz, granting her the power of the Titans. The Subjects of Ymir are called the "spawn of the Devil" (悪魔の末裔 Akuma no Matsuei?) because of this belief.
In all illustrations depicting the Devil, it is shown as a large, crouching figure with a menacing smile. In the book Frieda Reiss reads to Historia, the Devil is covered in a large cloak and hood, whereas in the book Grisha's father reads to Grisha, its head is exposed, revealing two goat-like horns and a long tail. It also appears with sharp claws, large muscles, and pointed ears.
Over 1,800 years before the Fall of Wall Maria, a girl by the name of Ymir Fritz is said to have met with the Devil, and the two made a deal. It is unknown what Ymir offered the Devil, but in return it granted her immense power, turning her into the first of all Titans.
At the time when Historia Reiss, a direct descendant of Ymir Fritz, was growing up on her family's farm in Wall Sina, her half-sister Frieda Reiss visited her frequently, teaching her important life lessons such as reading and writing. Occasionally, Frieda would teach Historia the story of Ymir and the Devil; however, in this story, the girl is named "Christa" instead of Ymir. Frieda instructed Historia to be a loving and beloved girl as "Christa" was.
In the year 850, when the Scout Regiment discover Grisha Jaeger's basement, they find three journals. Within Grisha's writings, he recounts his childhood, when he was told the story of Ymir and her deal with the Devil by his father.