Arioch ("fierce lion") appears in the Book of Genesis as the "King of Ellasar," who participated in the Battle of the Vale of Siddim, where the cities of the Jordan River plain revolted against Mesopotamian rule 13 years after the destruction of Sodom and Gomorrah. The battle consisted of four kings, led by Chedorlaomer of Elam: Amraphel, Arioch, Chedolaomer, and Tidal. They engaged in a punitive expedition against five kings of Canaan who rebelled against Chedorlaomer: Bera, Birsha, Shinab, Shemeber, and the king of Bela. The same story is also mentioned in the Book of Jubilees, where Arioch is called "king of Sellasar."
Arioch is also a fictional devil of vengeance and chaos in Paradise Lost. Originally the guardian angel of Enoch, when the morning star Lucifer (or Satan) had started to rebel against God, Arioch followed and became a fallen angel.
"Origin: Israel. A demon that presides over swords and chaos. He is also said to be the demon that holds sway over revenge. In Hebrew, his name means 'Fierce Lion' or 'One Like a Lion.' He was Enoch's guardian angel, but fell from grace when the angels revolted. He is the keeper of demonic swords, such as Storm Bringer. He appears as a being with black bat wings, with a flaming torch and a bloody axe."
—Shin Megami Tensei A-Mode DDS dictionary
Along with Surt and Astaroth, Arioch is one of the three major sub-bosses of the last arc of the game and one of the most powerful demons under Lucifer's orders that has taken control over the inferior part of the Basilica.
He appears in the fourth floor basement, fighting anyone that follows the will of YHVH because of his feelings for vengeance over "[what He] did [to him]." It is unknown what he means, but he is probably referring to his grotesque appearance, suggesting that it was caused by some kind of punishment from God.
In Chaos route, after locating the throne room of Asura in the eighth basement, the protagonist will need to go back to Arioch's room, where he will give him the "Arioch's Fang," a valuable item needed so Asura can forge the "Devil Ring" and make the fight against Michael and his followers become available.
Shin Megami Tensei V
"The fallen angel of Israel and the demon of vengeance. His name means "ferocious lion" and he is said to aid in vengeance of those who seek his service. During his time as an angel of God, he was recognized as the guardian angel of the saint Enoch. It is said that his name originally belonged to one in either the Book of Genesis or the Book of Daniel, only to become associated with the demon thereafter."
—Shin Megami Tensei V lore
Arioch serves as the Demon King and leader of chaos, trying to undermine Bethel at every turn. When his castle is revealed, Bethel forces quickly invade, although Arioch himself easily slays their lesser soldiers. The protagonist confronts him after he had finished exterminating a group of angels, where he realizes that they are Nahobino, although upset that they follow Bethel. Despite his best efforts to kill them, he is mortally wounded, realizing the power of a Nahobino and that the protagonist alone had the ability to decide the world's fate, imploring him to bring freedom in the name of chaos for the starving world before dying.
Majin Tensei II: Spiral Nemesis
Arioch is an optional boss on the Neutral Route in Paranoia, where he guards the base in the city area of Tebel.
Devil Summoner 2: Raidou Kuzunoha vs. King Abaddon
Arioch is one of the three demons summoned by Lucifer that must be fought during the New Game PlusCase File7th Trumpet, Eternal King.
Devil Survivor 2
"A fallen angel of Judeo-Christian lore representing vengeful spirits. His name means "Fearsome Lion." It's said that he only helps get revenge for those who hire him. When he still served God, he was entrusted with the protection of St. Enoch. He is originally mentioned in the books of Genesis and Daniel, but somehow he came to be known as a demon."