Samael occupies a genuinely inconsistent place across Jewish sources, and the inconsistency is worth keeping rather than resolving into one identity. In classical rabbinic literature he most often appears as an angel of death and an accusing prosecutor in the heavenly court, a difficult and even dangerous figure but one still operating within, and subject to, divine authority, not an independent enemy of God.
Later kabbalistic literature, especially the Zohar, develops him considerably further, pairing him with Lilith as a demonic consort and giving him a more autonomous role within a cosmic structure of evil, closer to what later folk tradition means by a devil. Popular usage since the medieval period has often simply equated Samael with Satan, but that equation flattens real differences between the earlier, more restrained rabbinic accusing-angel figure and the fuller, more independently malevolent kabbalistic and folk figure that developed later.
Because Judaism has no single authoritative narrative source comparable to a gospel for this figure, comparable instead to the ways Christian tradition would eventually assemble one composite Satan from several biblical figures, Samael's character was built up gradually across midrash, Talmud, and mystical literature over many centuries, and the different layers were never fully reconciled with each other into one settled portrait.