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 cataclysmically powerful Dragon Slayer that can take the form of a Dragon, that assaulted the Fairy Tail core Mages on Tenrou Island in the Year X784.

Appearance
Acnologia's preferred appearance is that of his human form, which is that of a rather muscular young man with long, dark blue colored hair. He carries a sharp gaze; his eyes have black circles around them. He is dark-skinned, and on his body he bears the same light blue markings he does when he is a Dragon. For attire, Acnologia dons a high collared, black cloak (which also bears his draconian markings), sharp red claws around his neck, a sash around his waist, a gold arm ring tightened around his right upper arm, and baggy pants which are decorated the same as the most former article of clothing.

As a Dragon, Acnologia is mastodonic, and has an entire upper body covered in black, round, scales, which, in turn, are decorated by spiraling, blue markings. His lower body, specifically his chin, chest, stomach, inner tail, thighs, and arms, 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, and very similar to fellow Dragon Grandeeney's. The scales disappear at the end of Acnologia's tail, which, in itself, ends in a stinger-esque shape.

Personality
Four hundred years ago, Acnologia was a ruthless, bloodthirsty and violent person. He killed any and all Dragons he could, ignoring the fact that many were his comrades.

In the present, Acnologia is a recluse who wants nothing to do with humans, in spite of the fact that he is one. As Zeref Dragneel puts it, he sees other humans as nothing more than insects, ignoring any and all attempts by them to converse, which suggests that Acnologia is highly arrogant. However, inversely, Acnologia's motives are also shrouded in mystery, as even with one arm he, according to Zeref, has the power to rule the world yet elects not to do so. Insights into his wishes have only been touched upon by outside sources, which include his vague desire to fight against humanity, as well as face an opponent strong enough to give him a real challenge. Ultimately, in a form of irony, despite his inherent hatred for humanity, Acnologia prefers to take on the shape of his old human form in casual instances.

While in his Dragon form he has shown to be very destructive and violent as described before in legend, in his human form, Acnologia retains a stoic and composed personality, even after striking down God Serena, Acnologia still maintained his stoic composure. However Acnologia possesses a love for battle, as Zeref theorized he was looking for a worthy challenge and let out a smile after Zeref promised him he will soon have a worthy fight. When Acnologia comes across strong opponents, he shows a more excited side to himself, such as during his fight with Irene Belserion he smiled with excitement and anticipation after witnessing the power of the Shield of Spriggan, even giving her praise.

History
Born over 400 years ago, Acnologia was one of the first Dragon Slayers to come into being, entering the Dragon Civil War on the side supporting coexistence. Acnologia and a group of other Dragon Slayers, however, disregarded the cause their comrades fought for, and killed every Dragon they could, bathing in their blood. Due to the overuse of his Magic, Acnologia's physique eventually turned into that of a Dragon's, and he proclaimed himself to be the Dragon King. This event was forever etched into history as the Dragon King Festival.

For many years, Acnologia roamed Earth Land, reputed as a fearsome Dragon, and was credited with the single-handed destruction of an entire country. At some point in time, Acnologia ran into Gildarts Clive when the S-Class Mage was on his "100-year quest" on Zonia Mountain. In an instant, Acnologia took Gildarts' left arm, left leg, and an internal organ, leaving him to die, before flying away. Gildarts, however, managed to survive, albeit with difficulty, leaving him as the first human to ever see Acnologia and live to tell the tale.

Tenrou Island arc
Seemingly beaconed by Zeref, Acnologia arrives on Tenrou Island, wreaking destruction in his wake. Sensing the destructive capabilities the Black Dragon possesses, Makarov Dreyar enters Giant mode, attempting to hold the Dragon at bay to allow the other members of Fairy Tail to escape. After a brief struggle, Acnologia, taking advantage of Makarov's previous injuries, knocks the Guild Master to the ground, pummeling him with his claws.

Just as he is about to kill Makarov, Natsu Dragneel latches onto Acnologia, preventing the killing blow. Despite Acnologia's attempt to rid himself of Natsu, the Fire Dragon Slayer remains latched onto the Black Dragon's scales, demanding that he leave their Master alone. Led by Erza Scarlet, the other members of Fairy Tail return, aiding Natsu in his assault against the Dragon. As Gildarts notes that Acnologia is simply toying with them all, the Dragon flies into the air, and then proceeds to seemingly obliterate Tenrou Island with his Dragon's Roar. After the deed is done, Acnologia soars off into the distance.

Tartaros arc
Acnologia appears again at the ruins of Cube where the battle between Fairy Tail Mages and Tartaros takes place. As he nears his destination, both Mages and the Demons take notice of his presence. Effortlessly, Acnologia creates huge explosions with his breath and shockwaves with his wings alone, much to the Mages' despair. He approaches Mard Geer and the Demon deduces that the Black Dragon is after E.N.D. However, Acnologia's rampage is temporarily interrupted, as the Fire Dragon Igneel, released from within Natsu's body, attacks him, with an intention to stop his rampage. Acnologia and Igneel begin to clash, while all the Mages below watch in horror and awe. After Natsu jumps on Igneel, the latter fires a huge flame blast towards Acnologia, although the beast easily shrugs off the attack and comes out of it unscathed. Acnologia is then later punched by Igneels' version of Fire Dragon's Iron Fist, however he shrugs this attack off as well.

Shortly thereafter, taking advantage of Igneel's worry for Natsu, Acnologia fires a Dragon's Roar at his opponent's head, but misses. Acknowledging Igneel as his enemy, Acnologia speaks to him, citing his displeasure at the existence of Dragons; he ends his comment by saying that he will slay Igneel. As the fight goes on, Acnologia tells Igneel that he won't escape. However, the latter explains that he didn't intend to run, and that he moved so that he can fight without holding back, in order to defeat the other creature. Acnologia, however, says that it won't be a simple defeat, but a one-sided obliteration. Later as the Face bombs across the continent begin to detonate, Acnologia is sent plummeting towards the earth extremely wounded, much to everyone's surprise. His body is then used as a victory stand by Igneel, who announces the arrival of the other Dragon Slayers' foster parents to stop the mighty threat of the Magic Pulse Bomb.

Acnologia doesn't stay down for long though, as he slashes out at Igneel and takes their battle back up into the sky. There, he questions Igneel's motives for having the other Dragons hide inside their foster Dragon Slayer children, and, when Igneel asks if he is scared of E.N.D. reviving, berates the Fire Dragon and declares that all he wants is utter destruction. Acnologia quickly overwhelms Igneel and repeatedly crushes his torso with his claws whilst screaming about destruction; he also derides the Dragon for being the Fire Dragon King yet not being able to fight equally with him and continues his relentless assault. Acnologia is then quickly overtaken by Igneel and loses his left arm, however in return, Acnologia destroys nearly the entire left half of Igneel's torso and then kills him with his Dragon's Roar. With his arm gone and his target slain, Acnologia then leaves Magnolia.

Avatar arc
One year after losing his arm to Igneel, Acnologia accepts Zeref's proposal to meet, and does so at an undisclosed rocky terrain, albeit in his human form instead of as a Dragon. Acnologia asks what Zeref wants; however, he is met with curiosity, as Zeref points out that Acnologia could rule the world with his power if he wished, calling his motives unfathomable. Acnologia, however, says the same of Zeref's motives. He then listens as Zeref tells him that he will not join or fight against Acnologia; rather, he will kill Acnologia along with everyone else in the world. He further implies that Acnologia has been waiting for someone to give him a true challenge and Zeref claims that he will gladly take on the role of challenger for Acnologia. Acnologia then gives a sly grin as Zeref tells him to wait for the ultimate clash between human, Dragon, and immortal to approach.

Alvarez Empire arc
Still residing in the cave where he and Zeref conversed last, Acnologia mentions that where his stolen arm was hurts; adding that he will destroy everything at the Dragon King Festival, he gets up and takes on his Dragon form, after which he shouts that he is the true "Dragon King". As he proclaims his supremacy, a strange, shadow-like substance extends from where his left arm used to be.

Acnologia, in his human form once again, later appears at the eastern war-front on Ishgar, just outside the borders of Bosco. There, he stands before three Shields of Spriggan—Jacob Lessio, August and God Serena—the latter having just ended his battle against the remaining Gods of Ishgar, as well as Jura Neekis. Claiming that he can quite clearly smell the stench of a Dragon, Acnologia challenges God Serena, with the Shield of Spriggan seemingly over the moon about finally encountering the "Dragon King". Before God Serena can finish his rant about how difficult it had been to find him, Acnologia suddenly attacks, tearing a hole in the side of his stomach with a single swift swipe of his hand. As the surrounding Mages watch on in awe, Acnologia proceeds to casually walk away from the scene, leaving the collapsed body of God Serena behind. As he takes his leave, he reveals his motive, stating that there are still seven more Dragon Slayers left, indicating that he intends to annihilate each and every one of them, until all remnants of the Dragons have been wiped out of existence.

Acnologia begins his trek to the northern battlefield at Zonia; along the way, he senses Gajeel's "death" and declares that only six Dragon Slayers remain, however, he is intercepted by Irene Belserion, whom he tries to dismiss. The Spriggan 12 member instead opts to block his path, prompting Acnologia to question her knowledge of him and wonder aloud whether she can even put up a fight against him.

Acnologia is almost immediately struck with a high-level enchantment from Irene (the Magic of which he recognizes); although taken aback at first, after realizing that Irene is a High Enchanter, he becomes excited and enthusiastically attacks her, in turn, with his Dragon Slaying Magic. After the dust settles, Acnologia praises Irene for her skill, but after Irene praises Acnologia for his power as well, she insinuates that Zeref will be more powerful than him once he attains Fairy Heart. The Dragon King and the Spriggan 12 member then briefly bicker back and forth until Irene decides that she is going to end Zeref's "game" of a war by utilizing a type of Magic that even Acnologia doesn't recognize. Irene informs him that it's a new type of Magic, and that she is enchanting the land of the entire Kingdom of Fiore; Acnologia asks for Irene's name, and after he is given it, he, and the entire kingdom, are enveloped in the light of Universe One. As a result of this, Acnologia is warped somewhere far away from the shrunken landmass that is Fiore.

Magic & Abilities
Dragon Slayer Magic (滅竜魔法 Metsuryū Mahō): As one of the first humans who entered the Dragon Civil War, Acnologia was also among the first Dragon Slayers brought into existence. Over time, however, as he slew many Dragons, he himself was, eventually, turned into a Dragon due to the extensive overuse of his Lost Magic. While it is currently unknown exactly which element Acnologia employs in his casting of Dragon Slayer Magic, it grants him the ability to reap the very souls of Dragons, leaving them in a half-dead state.
 * Dragon's Roar: Like all Dragons and Dragon Slayers, Acnologia can perform a Dragon's Roar, incorporating his respective element into a massive breath attack. While, as mentioned, which element Acnologia employs is currently unknown, said blast, while he was a Dragon, was potent enough to "completely eradicate" the entirety of Tenrou Island and imprint a giant crater into the ocean.

Shape-Shifting: Acnologia, contrary to the legends surrounding him, did not entirely become a Dragon and has retained the ability to enter and exit his extremely powerful Dragon Form at free will.
 * Flight: As a Dragon, Acnologia possesses the ability to fly, using his large wings to travel great distances, maneuver high up in the air, and perform aerial assaults on those below him.
 * Enhanced Durability: Acnologia, while a Dragon, is capable of shrugging off attacks from extremely powerful Mages like Erza Scarlet, Laxus Dreyar, and Mirajane Strauss, as well as from Natsu Dragneel, Gajeel Redfox, and Wendy Marvell, the latter three using their Dragon Slayer Magics, all their Magics having absolutely no effect on the Black Dragon. Later on, it is shown how even other Dragons of Igneel's caliber have high difficulty harming Acnologia in any noteworthy way, him taking the full force of Igneel's massive fire breath attack and emerging unscathed as if nothing happened. However, it should be noted that Igneel had already had his soul taken by Acnologia and was in a severely weakened state when the two of them fought.
 * Enhanced Strength: Given his immense size, Acnologia, in Dragon form, is easily capable of reducing a substantially sized area to rubble by simply landing on top of it. Truly attesting to the form's immense brutish strength, Acnologia engaged in a head-on physical confrontation with Makarov in his Giant form and easily gained the upper hand. According to Gildarts Clive, despite the amazing physical feats Acnologia performed on Tenrou Island, the Dragon wasn't using the same level of strength as he was during their brief confrontation, that rather, the Black Dragon was toying around with every last one of them.

Immense Strength: Acnologia holds tremendous raw strength even in his human form, as showcased when he slayed God Serena, the infamous strongest Mage of Ishgar himself and a Shield of Spriggan, with a single bare hand alone, ripping right through his abdomen and killing him in one swipe almost instantly.

Immense Speed: While only in his human form, Acnologia has been shown to move at blinding speeds, striking down God Serena before he or his spectating fellow Shields of Spriggan, August and Jacob Lessio, even knew what had happened.

Enhanced Smell: Acnologia has an incredible sense of smell, which he shares with other Dragon Slayers. He could instantly tell God Serena was a Dragon Slayer after smelling him from a distance and could tell there were 7 other Dragon Slayers across the whole country Fiore, despite the incredible distance between all of them.

Manipulation Immunity: According to Future Rogue, Acnologia is immune to Dragon Supremacy Magic.

Immense Magic Power: While only in his human form, Acnologia's Magic Power was said to be absolutely overwhelming to the point of even members of the Wizard Saints and Spriggan 12, even the strongest male, "Magic King" August himself, being awed and sweating at his enormous power. The strongest female member of the Spriggan 12 Irene Belserion even stated that he was more powerful than she initially thought. August even said that Zeref could only face him with the Fairy Heart's power. Much stronger than initially assumed to be, even after apparently going toe-to-toe with Igneel, the "Fire Dragon King", in combat (although Igneel's power was quickly dwindling due to the years he was sealed), Acnologia is mentioned by Zeref to be still waiting for someone to truly challenge him, implying that he was possibly holding back in his bout with the Fire Dragon King. Additionally, Zeref at one point has stated that Acnologia could rule the world with his power (which he was able to do in Future Rogue's timeline ).

Quotes

 * (To Igneel) "To think that Dragons still live... I am displeased."
 * (To Igneel) "I recognize you as my enemy, Dragon. And I shall slay you."

Battles & Events

 * Dragon Civil War
 * Team Tenrou vs. Acnologia
 * Igneel vs. Acnologia
 * Irene Belserion vs. Acnologia