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.

Appearence
Acnologia is a gargantuan, mastodonic Dragon whose entire upper body is covered in black, round, scales, which, in turn, are decorated by spiraling, blue markings. His lower body, specifically his belly, inner tail, and legs, are gray 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 his chin, is a protrusion that resembles an arrowhead. His large wings are feathery in appearance, akin to a bird's. The scales disappear at the end of Acnologia's tail, which, in itself, ends in a stinger-esque shape.

Birth of Shinseijū Tree
Born as a Dragon over 400 years ago, Acnologia was one of the first creatures in Ancient Izumo. For many years, Acnologia roamed Earth Land, reputed as a fearsome Dragon, and was credited with the single-handed destruction of an entire country.

End of Creation Arc
After Yuri no Mikoto ate the fruit of Shinseijū, Acnologia proclaimed himself to be the Dragon King. This event was forever etched into history as the Festival of the Dragon King.

Meeting a Jinjuriki
Acnologia arrives on Izumogakure, wreaking destruction in its wake. Sensing the destructive capabilities the Black Dragon possesses, Paul Gekko manages to subdue the dragon by using the Shadow Rasengan. After a brief struggle, Acnologia, taking advantage of Paul Gekko's Rasengan, absorbed the Chakra from the rasengan and befriends the Jinjuriki of the Yamata no Orochi.

Trivia

 * Acnologia is based on Fairy Tail's Beast with the same name.