Mard Geer Tartaros (マルド・ギール・タルタロス Marudo Gīru Tarutarosu) was an Etherious and the true founder of Tartaros, having used the Book of E.N.D. to unite the Etherious for a common cause, the revival of E.N.D. and the subsequent murder of Zeref. Cold and calculating, Mard Geer was a Demon that usually displayed no emotion, considering it a negative human trait, a trait of species that he thought of as inferior. He was capable of besting his enemies with powerful Curse, taking advantage of his Thorns, Alegria and even the Ultimate Curse, Memento Mori.