|Children of the Devil! I'll kill every last one of you!|
|— Bertolt Hoover declares vengeance on the Eldians on Paradis|
The Earth Devil (大地の悪魔 Daichi no Akuma?, also translated as the Devil of All Earth or the Devil of All Land) was 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 "children of the Devil" (悪魔の末裔 Akuma no Matsuei?) because of this belief.
The world was convinced that the Earth Devil was real, slain by the Marleyan hero Helos during the Great Titan War, until Willy Tybur revealed that the story of Helos is mere propaganda. Eren Kruger suspected that Ymir's deal with the Devil was fabricated by the enemies of her people; although, the tale is told in an Eldian book as well.
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 Mr. Yeager 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.
In a bronze statue in Liberio depicting Helos slaying the Devil, he takes on a much less demonic appearance, becoming more Titan-like with a thick beard and a full head of hair, lacking visible horns.
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. Eren Kruger later claimed to Grisha Yeager that this myth was false, and that he believed Ymir had in reality discovered the source of all living matter, where she gained the power of the Titans. However, Kruger also claimed that there is "no such thing as truth in this world," indicating that it is possible for neither story to be true, as both contradict each other and tell a different tale.
At the time when Historia Reiss, a direct descendant of Ymir Fritz, was growing up on her family's farm in Wall Sheena, 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, instructing her on how to be a loving and beloved girl as Ymir was.
Some years later, when the Survey Corps discovers Grisha Yeager'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 as well as Kruger's revelation of the falsehood behind the myth.