One of the polemical tools used by the 2nd century Christian authors in disputes with the heretics is to define them as „children of Satan” (or, in reverse, identifying Satan as their „father”). According to the author of this text, this is by no means empty invective, but polisemic category, whose polemical force requires decoding. The purpose of this paper is to hypothesize about its sources in the hermeneutic tradition and its importance as an “argument” used against ideological adversaries. The reconstruction of these dimensions will be made on the basis of the speech against Mark the Gnostic which was delivered by an unknown (probably Asiatic) presbyter and preserved in the first book of Adversus haereses (15.6) of Irenaeus of Lyons. In the opinion of the author of this paper, naming heretics as children of Satan has its source in the targumic and midrashic interpretation of Gen 4.1, according to which Cain was not the child of Adam but of the Satan-serpent. If this intuition is correct, the polemical force of this phrase would lie in the stock of the negative associations, anchored in the myth of Cain – fratricide, who shared murderous intent with his father, satan.