Tannin

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

Appearance
Tannin normally appears as a purple Western Dragon that is 15 meters tall.

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 rankers 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 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.

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.

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

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

Trivia

 * Tannin means Dragon in Arabic (تنين).
 * 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 and only 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.