In the cosmology the Apocryphon of John lays out, the true divine source generates a series of paired emanations, the aeons, that together make up the fullness, the pleroma. Sophia is the last of these, and in her longing to know the ineffable source directly, without her partner aeon, she conceives and brings forth a being on her own, a violation of the pattern that governs everything above her. What she produces is misshapen, a form with the face and body of a serpent crossed with a lion, radiant with fire yet without the fullness's light behind its eyes. Horrified at what she has made, Sophia hides him away in a cloud outside the divine light where none of the other aeons can see him, and the being she has cast out grows up alone, entirely ignorant that anything exists above or before him.
Other Gnostic sources vary the details, some naming Sophia's error differently or placing other figures at points in the sequence, but the core claim holds across the Sethian material: the maker of the visible world is not the highest god but an accident of a lower power's isolation, produced without the knowledge or consent of what stands above it.