Samael is one of the most ambiguous figures in Jewish angelology, a great and dread being whose name is often read as "the venom of God" or "the severity of God." He appears on both sides of the moral line at once. In some texts he is a legitimate angel of the Lord, a prince of the heavenly host, an agent of divine judgement and, in some traditions, the guardian angel of Esau/Edom, that is, of Israel's adversaries. In others he is the chief of the satans, the accuser and seducer, identified with the serpent of Eden or its rider, the angel of death, and the tempter of humankind.
Kabbalah systematized this darker aspect, making Samael the masculine head of the demonic "other side" (sitra achra), consort of the demoness Lilith. The figure's doubleness is the point: he embodies the way severe judgement and destructive evil shade into one another, the harsh face of divine justice that, pressed too far, becomes an adversary. He is a prime example of how Jewish tradition, reluctant to grant evil full independence from God, produced beings who are at once servants of the divine order and its most dangerous opponents.