Acnologia

Acnologia (アクノロギア Akunorogia), also known as The Black Dragon (黒龍, Kokuryū), and fearsomely reputed as The Black Dragon in the Book of Apocalypse, is a powerful Dragon that appears to be flying around the continent or the world. He seems to have some connection with Zeref; the depths of this relationship are as of yet unknown.

Appearance
Acnologia is a mastodonic dragon whose entire upper body, is covered in black, round scales, which in turn are decorated by spiraling, blue markings. Its lower body, specifically its belly, inner tail and legs, is grey in color, and seems to be rather smooth. It possesses a blunt, rounded head with four large and elongated plates extending backwards, and has white beady eyes. Its mouth is full of sharp teeth, and below it is an elongated protrusion pointing downwards. Acnologia’s gargantuan, multi-layered wings are composed of the very same plates covering its whole body, which take on a formation reminiscent of a bird’s feathers. Its massive tail splits in two at its end, where the black plates disappear, and takes on a double stinger-like appearance.

Personality
While the other Dragons appear somewhat friendly to humans, Acnologia is antagonistic towards them, and views them as insignificant. As Zeref puts it, it sees them as nothing more than insects pestering him.

History
Prior to the beginning of the story, Acnologia was already an infamous, feared dragon, being known for single-handedly wiping out an entire country. Acnologia ran into Gildarts Clive when the Mage was on his "100 year quest" on Zonia Mountain. In an instant, Acnologia took Gildarts' left arm, left leg, and an unspecified organ, leaving him to die before flying away, though Gildarts managed to survive, albeit with difficulty.

Tenrou Island arc
Acnologia comes to Tenrou Island, wreaks havoc on it, and fights the Fairy Tail members on the island. In the battle, it causes so much devastation that Makarov is forced to hold him off to allow the other Fairy Tail Mages to escape. As the two fight, Acnologia is eventually able to knock Makarov to the ground. Just as it is about to kill Makarov, all of Fairy Tail comes back and starts attacking the dragon. Acnologia then flies into the air, and seemingly destroys Tenrou Island, and all the Fairy Tail members on it with his Dragon's Roar. After these events, Acnologia takes back up to the skies and disappears from sight.

Magic & Abilities
Dragon Roar: As all dragons and Dragon Slayers, Acnologia can perform a breath attack of its element. It is unknown what such element is, but once it's fired in the form of a giant beam it is capable of causing a huge explosion, which was enough create a gigantic crater in the water. Flight: Being a dragon, Acnologia possesses the ability to fly, using its large wings to travel over long distances, manoeuvre high up in the air and perform aerial assaults on those below it. Immense Durability: Acnologia was shown capable of shrugging off all the attacks from the Fairy Tail members who came to Makarov's aid. Even those from Mirajane in her Satan Soul form and the ones from three different Dragon Slayers, whose Magic is supposed and thought to be able to harm dragons, were utterly useless against it. Immense Strength: Given its gargantuan size, Acnologia is capable of easily reducing a wide area into rubbles simply by landing on it after flying high up into the sky, and to engage in a physical confrontation with Makarov in his Titan form, injuring him in the process and eventually gaining the upper hand. Despite easily dominating the various Fairy Tail members, many of which possessing S-Class abilities, on Tenrou Island, Gildarts claimed that Acnologia was not using the same level of power it did back during their past confrontation, and that it seemed like it was just playing around with them.

Major Battles

 * Fairy Tail vs. Acnologia