Boreas

"Tremor Dragon King" Euros ["地滅竜王" エウロス, "Jimetsu Ryuu Ou" Eurosu] is an Earth Dragon King and the Guardian of the 96th floor of Ramiris’ Labyrinth.

Background
The dragon is an earth dragon.

Milim brought an adult earth dragon dungeon that she tamed, where it guards the 96th floor of the Labyrinth. It was allowed to make a nest and it feeds off of Veldora's aura for food.

From fighting in the labyrinth and absorbing Veldora's aura the dragon evolved into a dragon king class.

The dragon was granted a name by Ramiris and Rimuru gave them 5000 souls, which allowed it to evolve into a True Dragon King. Upon its evolution, it obtained a humanoid form, which is different from Milim's draganoid form in that Milim is a Spirit Form species, while the Dragons are a corporeal species that have changed forms (they are bound to their bodies). Though it had equal stores of energy to the Ten Lords of the Labyrinth, had lower fighting prowess, and thus decided to train in its new body.

Appearance
Dragon - 20 meter dragon (assumed).

Dragon King - 20 meter dragon (assumed).

True Dragon King - Beautiful Humanoid form.

Abilities
Earth Elemental Control.