Acnologia is a gargantuan, massive black Western Dragon whose entire upper body is covered in black, round, scales, which in turn are decorated by spiraling, blue markings. His lower body, rather his belly, inner tail, and legs, are grey in color, and appear to be rather smooth. Acnologia's eyes are white and beady, and his head is round and blunt with four, large, elongated, plates extending backward. Acnologia's mouth is full of razor-sharp teeth, and, attached to its chin, is a protrusion that resembles an arrowhead. His large wings are feathery in appearance, similar to that of a bird's and very similar to his fellow dragon, Grandeeney's. The scales disappear at the end of Acnologia's tail, which, in itself, ends in a stinger-like shape.
Before becoming a Dragon in appearance, he was a normal human. In time, however, Acnologia's appearance turned into that of a dragon which became known for by its current appearance.
Before becoming a dragon, Acnologia was considered to be ruthless, bloodthirsty, and violent. He indiscriminately killed any Dragon he could find regardless if they were his allies or his enemies.
When he became a Dragon, he became more reclusive and refused to go into hiding with several of his kind, while at the same time, want nothing to do with humans despite once being a human himself. According to Zeref, Acnologia does not want to interact with humans to which he believes are inferior and considers them annoying insects that are pestering him and would not bother to interact with them. This makes it seem that he is highly arrogant despite the fact he was once human.
HistoryBorn as a human over 400 years ago, Acnologia was among one of the first humans who became Dragon Slayers in which he and his fellow Dragon Slayers would participate in the Dragon Civil War. He and his fellow Dragon Slayers were selected in order to support the side that was desiring coexistence with humans. However, Acnologia and a group of other Dragon Slayers disregarded the cause their comrades fought for, and killed every Dragon they could and bathed in their blood. With what would be the aid of the Black mage, Zeref, Acnologia ended up becoming a dragon and as a result declared himself to be the Dragon King. This event led to the creation of the Festival of the Dragon King, to which it would forever be eitched into history.
For many years, Acnologia roamed Earth Land, while he became recognized as a fearsome dragon, and was responsible for his single-handed destruction of a continent. At some point in time, he encountered Gildarts Clive, the ace of Fairy Tail as the latter was going on his "100-year quest" on Zonia Mountain. In an instant, Acnologia attacked and successfully mutilated Gildarts to which he lost his left arm, left leg, and an unspecified organ. Acnologia left him to die and flew off but unknown to him, Gildarts survived the onslaught and became credited for being the first human being who ever survived Acnologia's wrath and lived to tell the tale.
Tenrou Island arc
After Zeref appeared on the Grimoire Heart Ship and killed Hades, Acnologia arrives on Tenrou Island where the Fairy Tail mages were taking their S-Class exams and begins to unleash destruction. As the Black Dragon was rampaging across the island, Makarov who sensed its destructive capabilities, entered into his Titan mode and tried to hold the Dragon at bay while telling his guildmates to run and leave the island. However as the Black Dragon gained the upper hand and was about to launch a fatal blow after pummeling the elderly Guild Msdter, Natsu decided to fight Acnologia together.Despite this interference, Acnologia tried to get rid of Natsu but he stayed latched onto its back. The others led by Erza followed suite and everyone began to attack the massive black Dragon. Despite the combined teamwork of all the Dragon Slayers and the mages, it was not enough to defeat the dragon as Gildarts noted that it was toying with them rather than going at the level of strength it did when it fought Gildarts. The Dragon flew into the air and charged its Dragon Roar, and when fully charged unleashed a tremendously powerful blast that seemingly destroyed Tenrou Island and all of the Fairy Tail mages. After the deed was done, Acnologia flew once again into the distance and seemingly disappeared without a trace.