Tannin

Tannin is the Purple Dragon and former Dragon King. Known as the Blaze Meteor Dragon, he was reincarnated into an Ultimate-Class Devil. He is the Dragon that trained Issei to obtain his Balance Breaker.

Appearance
A purple Western Dragon that is 15 meters tall.

Personality
Tannin has a warrior-like personality. Unlike the other Dragons who are selfish, Tannin cares for his fellow Dragons, willing to become a Devil to allow his race to continue.

History
Tannin is one of the Dragon Kings who once challenged the Great Red but was ignored. Some time before the series, he was reincarnated into an Ultimate-Class Devil. He became a Devil for two reasons: the first is to participate in Rating Games, the second is for the Dragon Apples, a fruit now existing only in the Underworld that a certain race of Dragons need to eat in order to survive, even making research on how to artifically grow the fruits.

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 Underworld 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 after Arthur Pendragon came to retrieve both of them with Tannin surprised 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 who is in cahoots 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 in 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 Midgardsormr knockout with ease. After the battle against Loki, he is seen ordering Issei in restoring the destroyed battlefield.

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

Power & Abilities
As a former Dragon King and an Ultimate-Class Devil, Tannin is an extremely powerful Dragon that is on par with the Four Satans. He is also ranked among the top 10 in the Rating Games. Tannin has an ability to transform into a mini Dragon form to fit into small places. As with many other Dragons, Tannin has the ability to breathe fire. His breath is said to have power rivaling a meteor strike.

Tannin also has the common powers of Devils.

Trivia

 * Tannin is famous among the children of the Underworld for his appearance in Rating Games.
 * Tannin's name originates from the Jewish sea demon Tannin, which is ironic in a sense that Tannin uses Dragon flames instead of water. It is also the modern Hebrew word for crocodile.
 * Tannin's peerage consists entirely of Dragons.