Entei

is a horse yōkai that obeys only the most powerful of yōkai.

Background
The anime gives some insight into Entei's background which was completely unexplored in the manga. Entei first appears to a rather powerful halberd-wielding ogre demon named Rengokuki who fought off hordes of demons with ease and a had a strong will. Recognizing his strength, Entei offers him his servitude and the two become a feared duo. Some time later, the demon is pacified by a powerful holy seal which is then destroyed by Hakudōshi. Entei reunites with his old partner and does battle with Inuyasha's group and is able to fend them off if only for a little while before fleeing. He later comes across Hakudōshi and challenges him, but he seems to be unable to even phase him. As the 'battle' drags out, Entei begins to second-guess Rengokuki's power and eventually throws him off his back, rejecting his old master and accepting Hakudōshi as its new master. Rengokuki is subsequently beheaded and the Hakudōshi takes his weapon as a prize.

From forward on, Entei is ridden by Hakudōshi for all of his future appearances until he is finally vanquished by Inuyasha with his Backlash Wave.

Powers

 * Speed: Entei is infamous for his rather astounding speed and appears to be as fast as Sesshōmaru.


 * Fire: Being a fire elemental, Entei is able to breath fire from his mouth, spitting fire balls or a stream of fire, similar to a flamethrower.


 * Flame burst: Entei used a powerful flame burst destroying the hill in which he was sealed.


 * Thunder: When concentrating, his demonic power can launch a very destructive and powerful thunder attack.

Trivia

 * It would seem that the fires on Entei's hooves won't extinguish when he's in water, just like Kirara's fire on her paws.
 * Entei shares its name with another fire-breathing creature, namely the Volcano Pokemon from the legendary beast trio of Generation II in the Pokémon games.
 * Entei looks very similar to the Pokémon Rapidash.
 * In one of the openings, Kirara is able to keep up with Entei.
 * The portrayal of Entei's death differs between the manga and the anime. In the manga, Inuyasha killed Entei and destroyed Hakudōshi's body with the Wind Scar simultaneously after Saint Hijiri broke Hakudōshi's barrier, while in the anime, the Wind Scar only hit Hakudōshi, after which Entei covered Hakudōshi's escape and engaged Inuyasha in combat, forcing Inuyasha to lure Entei into a cave to cancel out his speed advantage before slaying him with the Backlash Wave.

炎蹄