The King of Hell (冥府の王, Meifu no Ō) is a being that is used by a wielder of the Rinnegan. This figure, like the Animal Path's summons, possesses Rinnegan eyes, allowing a Rinnegan wielder to see through its eyes.
It is used by the Naraka Path for interrogation and is capable of discerning whether an individual is lying or not. When implemented on a target, a serpent-like apparition of their life force energy, in the form of an enlarged tongue emerges from their mouth and is presented to the figure. The King of Hell then proceeds to pass its judgement on the victim. If they are lying (or refuse to answer the question), their life force energy is ripped out by its two hand-shaped tongues and consumed, leading to the victim's death. If the target is telling the truth, it lets go of the protrusion leaving the target alive but extremely exhausted. The King of Hell can only be seen by the ones it's being used upon.
For its second ability, the King of Hell can repair the other Paths, should they be damaged or killed. When it consumed the remains of the Asura Path, the path emerged from the figure fully restored and was even wearing a new Akatsuki robe (the body had discarded its previous robe). While the King of Hell is being used for this, it seems that others are able to see it, unlike when it is being used for interrogation purpose. Both Naruto while in Sage Mode and Itachi Uchiha, who managed to blind it, were able to see it.
Lastly, it can be summoned for the Outer Path: Samsara of Heavenly Life Technique, where Nagato can release life force energy to people who were recently killed and allow their souls to return to their rejuvenated bodies. This technique can only be used by Nagato, the main entity in control of the seven paths. This power is said to transcend even the very concepts of life and death.
The King of Hell is based on the deva known as Yama, the judge of the dead who presides over the Naraka ("Hells" or "Purgatories") realm in the Hindu and Buddhist religion. He decided if someone stayed dead or returned to the world of the living, and would choose how they would be reincarnated. It's believed that if you lie to him, he will rip out your tongue.
The King of Hell's method of killing, which yanks the tongue out of the mouths of the Konoha shinobi that had lied, is a reference to a Japanese superstition that's used to scare children into telling the truth; "If you lie, Lord Yama will pull out your tongue" (「嘘をつくと閻魔さまに舌を抜かれる」, "Uso o tsuku to Enma-sama ni shita o nukukareru"). He also brought Kakashi's soul back from a purgatory-like existence.
- In the manga, the flames that surround the base of the King of Hell look similar to those of Amaterasu.
- The kanji on King of Hell's head means "king" (王, Ō).
- The card game calls him Heretical Icon.