Satan is a prominent figure in the Abrahamic religions, playing various roles in their literature. He may either be depicted as a rebel to the will of God, or as one who tempts mankind to commit sin to show God that mankind can easily be led astray from Him. In Judaism, particularly in the Book of Job and the Kabbalah, Satan is even able to take control of the life of a person in the stead of God, though only to the limited extent that God allows. Satan would appear to those who are sinful, playing into their hearts and towing them into despair. In Christian literature other than the Bible, when God commanded the angels to bow to the first human Adam, Satan (then an angel called Lucifer or Helel) rallied other angels against this command with the belief that angels are above all other creations. He and other "fallen angels" fought against the forces of God and were utterly defeated; as a result, Satan was cast down into hell.
Throughout the series, Satan serves as a servant of YHVH, with whom he also shares a philosophy of black and white. Satan is commonly associated with temptation of God, and is often portrayed as judgmental. Satan is also Lucifer's enemy, and they detest each other.
In Megami Tensei II, Satan is a former demon lord that is the manifestation of all the evils in the world. He disguises himself in Tokyo as Mr. Suzuki, the president of Suzuki Company Ltd., who can be met early on in his office located in the second basement of Ginza. There, he discusses the division between the two cults and the recent awakening of Lucifer. He also refers to the protagonist as 'the savior', just like the Messians.
Much later, after defeating Belphegor in his office, he appears before the hero, asking if he wants a drink. If he accepts a drink, he and his allies will have to fight Satan while paralyzed at the start of battle. Before the battle, Mr. Suzuki declares that he was the one behind the nuclear destruction of Tokyo. After Satan is defeated, if the hero recruited Lucifer, Mr. Suzuki's office will teleport you to a hidden part of the dungeon. This area, which also contains the Megiddo Fire, has a chamber which will send the hero to a secret corridor leading to YHVH.
Satan, better known as Zayin, is a member of the Temple Knights alongside Hiroko. He appears as a firm believer of the Center and a commanding officer for Aleph. However, he rebels after witnessing the tragedies that the Center inflicts upon the people of Tokyo Millennium and discovers the true nature of the Thousand Year Kingdom. Learning the flaws and lies of the center, Zayin dedicates himself of spreading the truth about the Center's machinations. It is also revealed that he is another of the Center's creations, designated to protect Aleph.
It is later revealed that Zayin is actually an incarnation of Satan, an instrument of YHVH's will sent to judge all creatures on Earth; both men and demons alike. He fuses with his other half (Seth) and transforms into his true form.
Depending upon the player's options, Satan plays either the role of an enemy or an ally. In the Neutral and Chaos alignment paths, he attempts to use the Megiddo Arc (a powerful laser weapon within Eden) to destroy all life on the planet as his judgment. He is killed by Aleph before he can carry out his plans, and his death prompts the appearance of YHVH. In the Law alignment path, Kuzuryu is unleashed, and Satan, fearing that it will destroy the Megiddo Arc, teleports Aleph, Hiroko, and himself to the Arc, which activates and destroys all life on Earth except the ones on the Ark. After that, he joins forces with Aleph and Hiroko to defeat YHVH after it wipes out humanity on Earth. Afterwards, having killed his creator, he crumbles to dust.
Satan is an optional boss on the Law and Neutral routes. He appears under the control of Lucifer and does not remember who is. He'll block the player from leaving His Excellency's tower, but then join the player upon defeat.
Satan appears as the final boss of the End of Days Ichigaya instance and was introduced as part of the game's eighth anniversary celebration. This Satan comes from a parallel world where he has destroyed the obelisks and wiped out most of the population, leaving the Setsu, Azura, and DB Kuroe of that world to seek out help from the main game world.
Unlike previous bosses, he is much larger and can be seen from the start of the instance. After defeating the Hallel forms of Ose and Flauros, players can take on Satan by restraining his hands and head, forcing him to battle them on a different plane.
The final boss of the game and the leader of the demonic invasion, and fought in chapter 59. He is still following God's orders, and despite God having long since abandoned the world, Satan continues to fulfill the role given to him to exterminate mankind. If the protagonist is not on the best ending's route, Satan will simply die, but if he is on the best ending's route, Satan will attempt to take the protagonist with him and fires a curse at him, which the heroine will intercept and take in his place.
Satan is a Persona of the Judgement Arcana. In order to fuse him, the player needs the Prosecutor's Diary Totem, which can be acquired by returning Anubis to the Velvet Room at MAX Rank. Upon being returned to the Velvet Room at MAX Rank, Satan produces Megido Fire, the most powerful shotgun in the game.
Satan appears as the ultimate Persona of the Judgement Arcana in Persona 2: Innocent Sin. He is the highest-leveled Judgement Arcana persona available throughout the game, capable of being summoned once the player reaches Lv. 91 or above. Satan, along with Lucifer, grants the most powerful Fusion Spell - Armageddon - which instantly destroys all foes regardless of their affinities, including all bosses.
Satan returns as the ultimate Persona of Judgement Arcana and one of the highest leveled personas in Persona 2: Eternal Punishment. His Material Card can be purchased in the Mu Continent for 50,000 coins after Ellen has left the party. Satan, along with Lucifer, is one of the ultimate personas of the game, only being available for summoning once the player has reached Lv. 91 or above. His unique Fusion Spell with Lucifer, Armageddon, is now ineffective against one Ultimate Boss. Casting this unto him will result in a counterattack, Armageddon R, which immediately wipes out all party members.
"The prince of darkness in Judeo-Christian lore, known for his role as the snake that tempted Adam and Eve at Eden. It is also said he is sent by God to test man's piety."
—Persona 3 FES Compendium
Satan appears as a Persona of the Judgement arcana. He is available to be summoned if the player has reached LV 78 or above. Lucifer (Helel in FES) and Satan's Fusion Raid, Armageddon, always deals 9999 Almighty damage to all enemies regardless of the target's defense, making it the most powerful spell in the game.
Satan appears as a Persona of the Judgement Arcana in Persona 4. He is available to be summoned should players have reached Lv. 76 or above. Interestingly, Satan's in-game model's color palette bears a darker hue and a stronger contrast compared to Persona 3. His portrait is more faithful to the original illustration in Shin Megami Tensei II, and prominently retains the 6 nipples which were edited out in Persona 3.
Satan makes an appearance as the Ultimate Boss in Digital Devil Saga: Avatar Tuner 2. He can be fought in the final dungeon, the Sun, where he attempts to deliver his judgment towards the party in the place of God. Unique from other bosses, Satan can only be fought under the Hard mode difficulty, or players transfer the Save Data of Digital Devil Saga: Avatar Tuner onto the sequel and select Hard Mode. His special attack is God's Breath, which is used every fourth turn and wipes out all party members. It can only be avoided if the player has at least one party member with max boosts to all stats (i.e. if the player's party keeps enacting the Charge combo spell), in which case Satan will use Dekaja instead. God's Breath can be survived with Close Call, although it's futile trying it, as Satan will merely cast it again.
Interestingly, Satan's attacks and speech during battle are reminiscent of his role and story in Shin Megami Tensei II, with him proclaiming God would force judgment upon Seraph and his assertion that a heretic was trying to destroy the balance of the universe. Besides, Schrödinger will state at the end of the battle he was only a memory and that the God he worshipped was different from the God awaiting at the final layer of the Sun.
In the final episode, Yamato, being pushed to his limits, makes a last stand as he dares Hibiki to kill him, fusing Nebiros and Zaou-Gongen to form Satan. Satan's attacks overwhelm Hibiki until he obtains his deceased friends' demons to fuse Lucifer.