Satan

Satan (a.k.a. the Devil) is an acient demonic spirit whom lives in Hell. Hell's Bowl as well as Hell itself. Anyone who dares to enter his domain he will immediately try to kill them and then eat them, no matter who it may be (he is a giant). He appears throughout the series to either be a foil to the heroes or provide some help.

Background Information
Satan was born roughly 300,000,000,000,000 years prior to the series began. He was said to be at least 545,863,213,193, 767 years old. Back then, he not only ruled Hell but ruled all of the Afterlife and the Homeworld as well. He plummeted the Homeworld into the Pit of Fires (also known as Hell's Bowl). However, his reign abruptly stopped after he was defeated at the hands of King Guru. He now forever lives in Hell and refuses to leave.

Date of Death
Due to being immortal and being a god, Satan cannot die. He is forever living, whether somebody "killed" him or not. The only way he can vanish forever is if he is destroyed in the Pit of Ash down in the Underworld. However, that has never even been attempted.

Carnage of Evil Saga
Satan is told in myths and fantasies by many others before his prolonged appearance. He finally appears sometime after Tadashi Sakura arrives in the Afterlife and he falls off of the path and lands straight in Hell, to where he planned on eating him. Satan and Tadashi began fighting as Satan wanted to eat him. Satan was way more than a match for Tadashi and so he was beating down on him. Eventually, Satan got fed up and sent Tadashi straight to the Underworld.

Dark Magician Saga
Satan later returns after Riku Hiroki's blood comes in contact with the Devil's Horns. Satan automatically is transported to where the heroes are and finds Tadashi and tries to kill him. Tadashi manages to trick Satan into killing both Sir Tekuma and Hydra. Satan is then later immobilized by the Dark Magician but is transported back to Hell.

Enter King Basoon Saga
Satan returns in the series finale of Sazeku-Ba!, where Riku travels to Hell and battles with Satan for a bit. Riku then tricks Satan and Satan shoots out a powerful blast straight for Sakabei Village. Riku then combined that with his own power. Satan is later seen killing King Basoon and then eating him.

Hell
Satan is the ruler of Hell so that means he controls all that goes down. He lives there, making that his home. He is not usually visited as Hell is a place filled with unimaginable pain. The fire that burns through the cracks in the walls and the grounds are hot enough to keep a person bruned for eternity. Because he is the King of Hell, Satan can control anything that goes on in Hell, no matter what it is.

Hell's Bowl
Along with Hell, Hell's Bowl is a side place right next to Hell. Despite being the ruler of Hell, Satan only rule's a small portion of Hell's Bowl as 98% of Hell's Bowl is ruled by Tarragon, who is the guardian of Hell. Even still, Satan is free to roam around Hell's Bowl as much as he likes.

Movies
Satan is one of many characters to not appear in many movies. However, he is one of the few secondary characters that appears in the movies. He makes his first appearance in the 7th movie.