Keep in mind that the demiurge being just "one person" is an assumption. My intuition is telling me that the demiurge – just like Lucifer or Satan – is not one being, but a way of thinking stemming from the source like every other idea.

https://en.wikipedia.org/wiki/Morgoth

"Before the creation of Eä and Arda (The Universe and the World), Melkor is the most powerful of the Ainur, the "angelic beings" created by Eru Ilúvatar. Melkor, dissatisfied that Eru had abandoned the Void, seeks to emulate his creator and fill the Void with sentient beings. This, however, requires the Flame Imperishable, the Secret Fire, which belongs to Eru alone; Melkor cannot find it. He contends with Eru in the Music of the Ainur, introducing themes of his own. He draws many weaker-willed Ainur to him. Ironically, these attempts do not truly subvert the Music, but elaborate Eru's original intentions: the Music of Eru takes on depth and beauty through the strife and sadness Melkor's disharmonies introduce. Unlike Aulë, Melkor is too proud to admit that his creations are made possible entirely by Eru. Instead, Melkor aspires to rival Eru."

It would be interesting though wether there actually is one being that got the idea first, and what this being is doing now.

The Gnostic idea of the Twelve Universes is also very interesting.

Here's a theory: The story of the demiurge is the story of the ISBE that created twelve prison planets. Every planet was lead by an "angel", which in reality is just the prison warden. For the prisoners, the prison is the whole universe, because they are not allowed to leave.

And while the prison planets where "perfect" in the beginning – at least perfect for the demiurge – the so called "flaw of the subordinate" emerged over time, which is the rise of the free will to leave the prison.

We should also remote view Sophia.