Tannin

Tannin is a Purple Dragon and a former Dragon King, known as the Blaze Meteor Dragon. He was reincarnated and became an Ultimate-Class Devil and helped train Issei in order for him to attain his Balance Breaker.

Appearance
Tannin is a gigantic Western Dragon standing at fifteen meters tall, whose bodily majority is covered with dark, purple scales. Tannin's lower body, specifically his belly, the inner portions of his long tail, and legs, is beige in color. Tannin has a triangular head with yellow horns, a pair of large, sharp eyes with lavender sclera. Tannin also sports very sharp canine teeth, and has claws with long, sharp yellow nails. Tannin's large wings resemble a bat's, with rigid tips. Additionally, he wears black armored shoulder pads that extends down to his arms and a loincloth decorated with metal accessories.

In his mini-Dragon form, he is similar in size to Asia Argento's Dragon familiar, Rassei.

Personality
Tannin has a warrior-like personality and dislikes those who are lazy. Unlike other Dragons who are generally selfish, Tannin cares for his fellow Dragons; willing to become a Devil in order for his race to continue.

History
Tannin, a former member of the Dragon Kings, once challenged Great Red to a fight but was ignored by him. Some time before the series, he was reincarnated into a Devil by Mephisto Pheles. He became a Devil for two reasons: the first was to participate in the Rating Games, the second was for the Dragon Apples, a fruit that now exists only in the Underworld, which a certain race of Dragons needs to eat in order to survive. He then joined the Rating Games, becoming one of the Top 10 and became an Ultimate-Class Devil where he gained the right to receive his own territory and chose the area where the Dragon Apples grew. He even started conducting research on how to artificially grow the Dragon Apples. Sometime before the series, Tannin entered into a semi-retired state from the Rating Games so that he could train the younger generation of Dragons.

Birth of the Breast Dragon Emperor
Tannin made his first appearance in Volume 5, where he trains Issei in one of the mountains in the Gremory Territory to help him attain his Balance Breaker. Afterwards, he and a group of Dragons who serve him take Rias's Peerage, Sona Sitri, and Genshirou Saji to the party for the Young Devils. Tannin later assists Issei during his fight against Kuroka and Bikou at the party for the Young Devils Gathering, which ended promptly after Arthur Pendragon came to retrieve both of them; surprising Tannin at the fact that the strongest Holy Sword, Caliburn, and its wielder are now under Vali Lucifer.

In Volume 6, Tannin fends off all the Devils from the Old Satan Faction who interfered in the Rating Game between Rias Gremory and Diodora Astaroth, the latter of which turns out to be working with the Khaos Brigade. He then confronts Ophis alongside Azazel. He and the Occult Research Club then witnessed the appearance of the Great Red who was floating through the Dimensional Gap. When asked by Issei whether they have fought before, Tannin said that he was ignored.

The Heroic Oppai Dragon
In Volume 7, Tannin was asked to help open the Dragon Gate to summon Midgardsormr, warning Vali that should he try anything weird, he will chew Vali. He later assisted in the battle against Loki, disposing of the smaller, mass-produced versions of Midgardsormr with ease. After the battle against Loki, he is seen ordering Issei to restore the destroyed battlefield.

In Volume 10, Tannin was one of the spectators of the Rating Game between the Gremory and Bael Team.

In Volume 12, Tannin and his followers faced off against one of the Bandersnatch, disposing of the monster easily.

The Legend of Oppai Dragon and his Lively Companions
Tannin visited the Hyoudou Residence in Volume 19 to ask for a favor to Issei and the people who govern the Kuoh Town. He asks them to take care of an egg of a Spectre Dragon, a particularly rare species, as the air in the Underworld is not suited for hatching the egg. Rias agreed to taking care of it and waited for the egg to be delivered. The egg was then delivered by Crom Cruach to everyone living in the house's surprise. Tannin told them to not be alarmed as he asked Crom Cruach himself to deliver it and he is currently living with him.

Power & Abilities
Immense Strength: As a former Dragon King and Ultimate-Class Devil, Tannin is an extremely powerful Dragon that is on par with the Four Great Satans.

Immense Durability: Tannin has extremely tough skin and could take Kiba`s Blade Blacksmith, Koneko`s punch and Akeno`s thunderstrike with relative ease.

Fire Breath: As with many other Dragons, Tannin has the ability to breathe fire. Tannin's fire breath is said to have the power rivaling that of a meteor strike.

Size Alteration: Tannin can transform into a mini-Dragon form in order to fit into small places.

Extending Horns: In the anime, Tannin has shown to be able to extend the length of his horns which can even counter Xenovia's Durandal and Kiba's Balance Breaker.

Flight: physically, Tannin remained as a Dragon and can fly with help of his dragon wings.

Trivia

 * In the anime and manga, Tannin stands on two legs; however, in the light novel, it's assumed that he stands on 4 legs.
 * Tannin means Dragon in Arabic (تنين). Tannin (Hebrew: תנין) also refers to a sea monster in Canaanite, Phoenician, and Hebrew mythology.
 * Tannin is famous among the children of the Underworld for his appearance in Rating Games.
 * Tannin's peerage consists of 10 Dragons.
 * He is the first male Queen that was introduced in the series.
 * Tannin is one of the two reincarnated Devils introduced in the series to have reached Ultimate-Class, the other one being the master magician Rudiger Rosenkreutz.