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, Satan is typically equated with Lucifer, who rallied other angels against the authority of God, intending to seize God's power for himself, after which they fought against the forces of God and were utterly defeated and cast down into hell, becoming demons.
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, the party will be teleported to a hidden part of the dungeon. This area, which also contains the Megido 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 is the true leader of the Monotheism faction, having split his essence into Merkabah and a version of Lucifer. The two halves lead a pointless eternal war between Law and Chaos to help YHVH maintain his power, but with the appearance of the Divine Powers, they quickly ally while maintaining the pretense of being separate beings to prevent the gods from destroying YHVH. He is eventually forced to re-fuse into one being, revealing that he has no motives of his own beyond serving the Creator, but he has secretly grown to doubt YHVH is worthy of the title. Realizing Nanashi and Flynn were chosen by the Great Will as messiahs, he tests Nanashi in combat and either (in the Anarchy ending) helping Nanashi destroy YHVH and become a more benign Creator, or (in the Peace ending) restoring life to Walter and Jonathan long enough to defeat YHVH, fully aware it will cause his own death.
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. There he will only confront the party, leaving behind the NPC support. This version can spawn megidoraon that act as separate enemies and is surrounded by Pneuma. He is the highest HP boss in IMAGINE to date with five times that of Demi-fiend.
In this final form, he will randomly select a member of the party as a sacrifice with the scapegoat debuff. If this party member does not kill themselves or the Seraphs that spawn around him at this point are not defeated within a few seconds, he will kill the entire party and inflict a massive HP debuff to all members. This form is also capable of sending the party to a different area where they will each have to face a room of Pneuma. After defeating their respective rooms, players have the option to help other party members clear their rooms or return to fight Satan. Party members who do not clear their rooms in time, including those who move to other rooms to help out, will be killed after a certain amount of time and receive a massive HP debuff. If this final form is not defeated within ten minutes, the party will be teleported out.
In defeating him without dying once, players can receive a unique item called God's Majesty, which can be used to upgrade equipment, modify weapons, enhance devil force, or be used as a powerful synthesis item. After defeating all three characters in a practice bout and defeating Satan, a true ending cutscene is unlocked, revealing that he was born through Kuroe's failure to protect the player character in that world. He takes on their form and attacks both Souhonzan and Arcadia.
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 fought on the Neutral route after beating Beelzebub, and resides in Amnesia's Eden. He is the final boss of the Light-Law route and fought on all routes. Satan seeks to fire the Helios laser at Megalopolis to destroy it. He succeeds on the Light-Law route, where Naoki and the others are sent back in time to prevent him from succeeding thanks to the angel Raziel.
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. He is also the only Judgment Persona that Reiji can use.
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.