The idea of evil supremacy on the material world is largely widespread in dualistic-Bogomil texts, but not all show the demiurgic process that leads the Devil to create the material world. The aim of our work is to illustrate the Devil's demiurgic activities within some documents, in use at the Bogomil and Cathar community, like the Secret Book and the Book of Two Principles (Liber de Duobus Principiis), the Sea of Tiberias and the Fight between Satanael and the Archangel Michael. In the mentioned texts, the creation is expressed in different way: in the only Secret book the material world creation is due to the Devil; the creator power of the Devil seems to be reduced in the other texts, which are contaminated by popular culture: it is underlined his predominance on the matter, and not on his creator abilities. In the Sea of Tiberias he creates the demonic armies (but in a Russian version of the apocryphon the element is lacking, therefore Satanail does not pursue any demiurgic activity); in the Fight between Satanael and the Archangel Michael he creates a second universe, pale imitation of that of divine origin (which includes the material world). The analysed works were probably born on Bulgarian soil, or otherwise have moved to Bulgaria. The Secret Book spread within the Italian Cathar community of Concorezzo (near Milan), and became one of the main texts; therefore we discuss in the appendix about another Cathar Lombard text, the Book of Two Principles: both are extremely important because they are among the few preserved texts, which describes in depth the Cathar doctrine; though their positions are very different (the Liber de Duobus Principiis is work of an absolute dualist), it may be interesting to compare them in order to demonstrate the diversity of the phenomenon in the same geographical area. In a further appendix we illustrate a very spread topic, occurring in the Sea of Tiberias: the extraction of the ground from the sea by the Demiurge, or an emissary of him, which often assumes the form of an aquatic bird.