Gnosticism portrays Demiurge as an inferior "evil" god who created the world who appears as the "God" of the Old Testament. He was also known by different Gnostic teachings as Adam Kadmon, Choronzon, Samael, Saklas, "Fool", or Yaldabaoth, "Son of Chaos". He is said to have been the devil, but some sects consider them to be two completely different entities.
In most schools of Gnosticism Demiurge was created by Sophia, exiled from the Pleroma for her desire to create something outside of it. When she created the Demiurge, she was ashamed by it; to hide her folly from the Pleroma, she created a great cloud around him and built him a throne. With no awareness of the Pleroma or the Monad from which all things were derived from, the Demiurge concluded it was the creator of all things. It then fashioned the material universe in an unconscious imitation of the Pleroma, and made the first human in the image of the true First Man. Though it could not grant him a soul (having no awareness of the Pleroma) Sophia pitied it and granted Adam a divine spark that gave him life. The Demiurge was infuriated when Adam thanked the true God for his existence instead of him and sought to ensnare him in the material world through Eve; however, Sophia sent the serpent to tempt Eve, granting her and Adam the secret knowledge of their spiritual nature. The Demiurge expelled them from Eden when he learned of this, and has since sought to keep the souls of mankind bound to the material world.
The concept of a Demiurge is that it is an artisan figure responsible for the fashioning and maintenance of the physical universe, but not the true creator deity. Though it is commonly depicted as willfully ignorant of the spiritual universe, the Demiurge itself and the material it uses to create and fashion the universe are considered uncreated and eternal or copies of the product of another being, depending on the system. In some of these systems, it and the rest of the material universe will be sent to Hell, where it will become the judge and torturer of the damned.
Known as Yaldabaoth, it is the ruler of Idea Space and resides in Paradise. In every route he is the final boss. During the battle against him his body loses the gold plating as it is chipped away with damage, revealing his true black body. His body is eventually destroyed, with his head detaching from it before its destruction and continues the fight.
"An imperfect god of Gnosticism who created the material world. According to Gnostics of the Roman Empire, the Demiurge proclaims himself as God; when Adam and Eve gain "knowledge," he cast them out in anger. The Demiurge wishes for the souls of humans to be trapped in the material world forever."
—Shin Megami Tensei: Strange Journey Compendium
Demiurge appears in the final EX Mission of Strange Journey, False God in Chains, as the game's Ultimate Boss. In this incarnation, he is a shard of the power of God, shattered from the whole after a battle with the Mothers of the Schwarzwelt, which resulted in Humanity opposing His will and making it harder for him to reassemble himself. Another fragment, a powerful angel, succeeded in convincing the Protagonist to kill Alilat, one of the wardens of the power, and open the sealed gate in the subterranean levels of Sector Grus to reach the immense monster holding the remains of the original power.
In the way to the hidden lair, a female voice will plead with the Protagonist to turn back. The voice will remain unheeded if one chooses to proceed to the final sanctum. Once both the Angel and the Protagonist reach Demiurge's lair, he will be invisible unless the Protagonist has acquired the final Enemy Search App from a rare forma in Sector Horologium. However, if the characteristics are met, Demiurge will appear, furious with the Angel and swatting him away, leaving only the Protagonist to confront the crazed monstrosity.
Demiurge does not only have the strongest elemental spells (Agi Gate, Bufu Gate, Zio Gate, and Garu Gate), but boasts Mahamaon, Mamudoon, Mother's Kiss, Dekunda, Heaven's Strike and Big Bang; additionally, it repels all attacks save for Almighty-type except a single type he is weak against (said type cycles through the battle), making him an extraordinarily difficult battle. In addition, he's fast and powerful enough to constantly evade most attacks and can even cast Diarama to give himself a hitpoint shield.
Following his destruction, he can be fused through Special Fusion by a combination of Metatron, Samael and Hachiman.
The female voice will speak once again as the Angel and the Demiurge's power are fusing, imploring the Protagonist to switch off his visor so she can seal off the two entities before they can successfully combine. This request can be indeed bidden, with the two being shut off in impotent rage as they are cut off from the Schwarzwelt.
However, if the Angel successfully absorbs the Demiurge's power, he gains the Demiurge's appearance and his name changes to "Refined Voice". Refined Voice warns that the true enemy is the spirit of Earth itself and, if the Protagonist fails to defeat it, he'll protect humanity himself as long as the souls of men are in tune with the Holy Spirit. If Law-aligned, the completed Demiurge will offer to join the Protagonist in his quest to destroy Mem Aleph and bring about the World of Law. The female voice will speak once again, lamenting that the destruction of the seal is a catastrophe, before becoming completely silent.
In either case, the Protagonist will be rewarded with the Chakra Elixir.
The Demiurge is the target of the Chaos-exclusive Challenge QuestThe Voice of Arrogant "Evil" given by Lucifer. Lucifer describes him in the quest details as an entity that broke away from God to rule a silent world. He is fought at the Sky Tower's 2nd Observation Deck, where his presence is warping the space around him. The Demiurge emerges from his realm, knowing that he has been forced to materialize and that Lucifer had "beguiled" Flynn, who he calls one of his creations, into opposing him, and notes that the fallen angel still relies on "cheap tricks".
He declares that he shall bring the lightning of punishment down upon the symbols of evil, demons, and mankind, intending to slay Flynn for straying from the path of justice. At the beginning of the battle he states that his lightning will course through them until nothing is left but ash.
As the Demiurge is defeated, he says that as long as Flynn is a child of man, he will remain a prisoner both in body and spirit, so he should give up, become silent, and be cursed, crumbling afterwards. Lucifer appears after the battle and is impressed at how Flynn defeated him and that he is the only human to have ever been able to handle his requests, and that with the Demiurge's destruction, Flynn's spiritual powers should have risen notably. Lucifer informs Flynn that the Demiurge was merely a Godly Spirit as a small part of the creator and that the true enemy is far greater.
Seichii Yamashiro is the Demiurge's human guise, an influential senator of Hirasaka City and one of the main driving forces behind the city's redevelopment project. The project, supposedly in the name of progress and modernity, would destroy many shrines built around the city which had been used to seal Inaruna's wrathful spirit. Yamashiro works alongside Sid Davis to capture Kumiko Hatano, who would be a vessel for Inaruna. When confronted by the protagonist in the senate chamber, Sid escapes into the Fake Astral Plane with Kumiko and Yamashiro reveals his true form as the Demiurge and attempts to kill him. However, the Demiurge is defeated and Rei Reiho teleports the hero to the Fake Astral Plane using the same magic circle that Sid used.
Yaldabaoth, the "God of Control", imprisons Igor in Mementos and impersonates him since the beginning of the game. After being discovered, he then takes the role of the game's final boss. He is the Conductor of the Conspiracy to put Masayoshi Shido into political power, and sponsored the Phantom Thieves as a thought experiment and game to see if their salvation of the world as is or Goro Akechi's desire to destroy and recreate the world was stronger. His true nature is hinted at throughout the game by his colder attitude than the real Igor, his voice, and his inability to perform Persona Fusions, relying on Caroline and Justine instead. Once he drops the act, he reveals himself to have a power-hungry, self-righteous personality with a tendency to toy with humanity out of sheer sadism. When Goro and later Shido are defeated, he decides that the world should be "saved", but due to his egotism believes salvation of the world is him taking control of existence and removing everyone with chaos in their hearts from it. He awakens his true body in the core of Mementos and summons a Palace that he later overlays over the physical world, granting him the ability to transform his lies into truth, influencing the minds of people into despair and complacency, and wiping away the existence of his enemies, as said enemies have left the cognition of the general public-and thus the fused reality itself. Only the recreation of Lavenza from Caroline and Justine's fusion, and the subsequent reawakening of Igor, manages to derail his plan, as Igor reveals that those banished from cognition do not die, but are sealed in the Velvet Room until someone with a strong bond releases them from the prison Yaldabaoth turned it into.
He is described as being the manifestation of humanity's subconscious desire for order, warped to the point where he no longer cares for the human cost or morality of said order; in his view, humans are little more than livestock and lemmings for him to rule over and command due to their self-destructiveness and stupidity. He initially takes the form of the Holy Grail, which starts off as black before the flow of wishes for him to dominate the world revitalize him and turn the cup gold. After the flow is cut off and the Grail defeated, the cup merges with his arena to become a giant version of his Shadows, a robotic, faceless angel who can manifest a gun, a bell, a sword, and a book in each of his four arms. When in human form, he appears identical to Igor, but his eyes turn white and glow when he admits his true identity, and he is prone to far more mocking facial expressions. After his true name is revealed Yaldabaoth never has a dialogue portrait in any of his forms. At the end of his fight, it is revealed he had enough power to defeat the Phantom Thieves at any time with his Rays of Control, but kept fighting them out of arrogance. Only by the intervention of Yuuki Mishima convincing people to send their wishes to the Phantom Thieves instead cuts off his power flow and allows them to stand up to his unsealed power.
Yaldabaoth harnesses the power of the deadly sins as proof of man's self-destructive nature during his boss fight. Satanael finishes him using a bullet harnessing the seven sins he condemns, putting a massive hole through his head. Shocked at the fact that he was beaten by a power that exceeded his own, Yaldabaoth realizes the true strength of the Trickster and ruefully acknowledges Igor's beliefs as he dissolves back into the original, mindless form of the Grail.
In Shin Megami Tensei: Devil Summoner and Persona 5, the Demiurge doesn't seem to have any connection to YHVH or his forces.
Although not connected to the YHVH who appears in the mainline series, Yaldabaoth represents the role of Law and the idea of YHVH in Persona 5, with the forces of Law like the four Archangels appearing as his heralds.
Yaldabaoth's "game" to decide whether or not humanity yearns for destruction and rebirth or to change via "rehabilitation" is similar to the game between Philemon and Nyarlathotep.
Philemon and Nyarlathotep's game was to probe the human mind, and decide if humanity could progress or be its own destruction.
Similar to how Philemon employed Persona-users who could prove humanity's potential and Nyarlathotep for individuals who used their power for self-gain, Yaldabaoth employed the protagonist, who wanted to change the world via "rehabilitation" in contrast to Goro, who wanted to "destroy the world and remake it anew."
The mechanical composition of both of his true forms in Persona 5 and using a book as one of his weapons may be a reference to Urizen, a character in William Blake's poetry who embodies dogmatic thought and logic as a tool of constraint as well as reason. Urizen is said to have defined the natural laws of the universe and is a patron of the sciences but at the same time said laws limit the universe and he dislikes individuality and imagination, which he cannot easily quantify. He is often described as wielding a codex of laws.
Yaldabaoth is the first antagonist to directly confront, defeat, and take prisoner Igor to control both the Velvet Room and the attendants.