Acnologia

Acnologia also known '''Black Dragon of the Apocalypse. '''He is a very recurrent antagonist in Fairy Tail, he is the main antagonist along with Zeref Dragneel, as well as the last antagonist to appear in Fairy Tail. He was a human and a Dragon Slayer who after killing countless dragons, himself becomes a dragon, he is totally determined to kill the Dragon Slayer.

Tenrou Island arc
Acnologia is first mentioned Zeref, when he punishes Hades for waking Acnologia. When Acnologia first appears in the form of a black dragon, he soon fights against Makarov who distracts him so the other members of Fairy Tail could escape the island, he is also seen by Meredy and Ultear when they escape Tenrou Island.

Avatar arc
A year after the fight against Igneel, Acnologia loses its arm during the fight against him. Acnologia accepts Zeref's proposal to be attacked on an undisclosed rocky terrain, however in its human form. Meanwhile, Zeref asks him that he could rule the world if he wanted with his power, but prefers not to. Acnologia however says the same thing to Zeref. Shortly thereafter, Zeref says he will not fight or join Acnologia, that instead he will all humans along with Acnologia. This then implies that Acnologia expected someone to give a challenge, Zeref then states that he will be happy to assume the role of challenger. After that, Acnologia gives a mischievous smile when Zeref says he will wait for the final confrontation between the human and the immortal dragon.

Alvarez Empire arc
After an Acnologia still in the cave and he mentions that arm has beem stolen and that it hurts, he then says he will destroy the Dragon King Festival, and gets up while taking on his dragon form. He shouts that he is the real Dragon King. After Acnologia goes to the eastern side of Fiore, he feels a dragon power, he comes across God Serena who is along with August and Jacob Lessio, as God Serena has one of eight dragon tears implied in him, then God Serena challenges him. However, Acnologia kills him with just a single blow. After Acnologia goes to Fiore where he sees Irene Belserion the two begin to fight and during the fight Acnologia is impressed with the powers of his magic, but she can teleport him away. After Irene's death, while Acnologia was walking he soon see Irene's dead body and begins to attack Irene's dead body and begins to attack Irene's dead body and begins to attack Irene's dead body, but Erza tells him to stop.