As one of the oldest phenomena in the universe, the concept of evil has always been the subject of interest of many nations around the world. Some of them have used it throughout history as a source of inspiration in order to create numerous literary works. Precisely this the Beowulf poet and John Milton have done by creating Beowulf and Paradise Lost, the epic poems written in completely different periods of time, but still sharing the same theme: the battle of good and evil. Interestingly enough, the characters of both poems are incredibly similar; and this especially applies to the main antagonists. The monsters of Beowulf, Grendel, Grendel’s mother and the dragon, can be compared to Satan, Beelzebub and Moloch, the fallen angels of Paradise Lost. Their evil nature is defined by three motifs used by both authors: the concept of the uncanny, the idea of dualism, and the blend of Christian and pagan cultural tradition. Moreover, the villains of an individual epic poem together form the “Triad of Evil”, the perversion of the Holy Trinity. In this way, the antagonists of Beowulf and Paradise Lost are of rather ambivalent quality: they have a dual identity and dual origins because both authors invoke the Old English tradition of combining Christian and pagan elements within a single literary work. Therefore, Beowulf and Paradise Lost are outstanding poetic achievements because they successfully guard not only the old literary tradition, but also the ancient concept of evil.