The purpose of this article is to show the semantic change that occurred in the case of Beelzebub. The basis for and at the same time the starting point for these considerations was the Old Testament term baal zebul. The term has its etymological and semantic parallels in other Semitic languages. The transformation of the name of this deity was likely due to the unbiblical Jewish tradition, which – in an attempt to put an end to idolatric practices – slightly changed the name, causing a tremendous change in meaning. The analysis performed in the paper allows us to establish that the change in the meaning was not a rapid one, but it was rather the result of a lengthy process in which the interference of the unbiblical Jewish tradition seems to be the first stage. In addition, it was found that factors such as: as the fight of monotheism with the worship of Baal, religious syncretism, the penetration of the Baal motif into the Old Testament, and dualism led to a situation in which the New Testament understanding of Beelzebub was an established view of Beelzebub as the demonic ruler.