E.N.D.

E.N.D., real name Etherious Natsu Dragneel, is one of the villains in Fairy Tail. He's an Etherious, the strongest Demon created by Zeref, and the Guild Master of the Dark Guild Tartarus.

History
Four hundred years ago, E.N.D., the strongest and vilest Demon born from the Books of Zeref, fought with Igneel, in which the Dragon failed to kill the Demon. At some point, the Etherious formed the Dark Guild Tartarus with E.N.D. as their Guild Master.

However, under unknown circumstances, E.N.D. was sealed back into his book with an unbreakable Magic seal four hundred years ago.

Abilities
It's said that E.N.D. is to be the most powerful demon ever created by Zeref. According to Gray's father, Silver, E.N.D. is a fire-type demon.

Tartarus arc
With E.N.D. in a dormant state, the Demons of Tartarus seek to revive their Guild Master by wiping out the Magic Power in the world and gathering Curse Power, and return to their creator Zeref's side.

After the destruction of Face, Kyouka reports to Mard Geer, who is holding E.N.D.'s book, requesting that they wake their master up, only to be told that there is too much Magic Power present in the world for E.N.D. to resuscitate.

Later, after the Tartaros Battle, Zeref unveiled that E.N.D.'s full name is actually Etherious Natsu Dragneel.