Devil of All Earth

The Daichi no Akuma (大地の悪魔) was a figure of Eldian mythology who made a deal with Ymir Fritz, causing her to become the first of all Titans. Beyond what the myths tell, the true nature of the Devil is unknown.

Appearance
In all illustrations depicting the Devil, he 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, his head is exposed, revealing two goat-like horns and a long tail.

History
Over 1,800 years before the fall of Shiganshina District, 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 he granted her immense power, turning her into the first of all Titans.

The Uprising arc
At the time when Historia Reiss, a direct descendant of Ymir Fritz, is growing up on her family's farm in Wall Sheena, her half-sister Frieda Reiss visits 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.

Return to Shiganshina arc
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.