Ben recently asked me about Evil in Greek mythology. There is no Satan in Greek mythology. No Iblis. No god of evil or manifestation of such. No horde of monsters gnawing at the roots of the universe. There is neither boogey man nor things that go bump in the night. And ghosts are rarities in the Ancient Greek mind.
If Death is called “evil” (Iliad 3.172, 22.296, 16.46, etc.) it’s not because Thanatos is a bad guy. He brings an end to pain and physical suffering. He is the twin brother of sweet Sleep. People call Death evil because they are not sure where he will take their disembodied spirits; the Isle of the Blest or Lord Hades’ dreary realm. If people speak of “hateful” Hades (Pausanias 8.18.3, Argonautica 3.806) and “dread” Persephone (Odyssey 10.490, Iliad 9.454) it’s because they hate and dread ending up in their realm. Lyssa (Madness) isn’t a baddie either. She actually objects to maddening Heracles in Euripides’ play of the same ilk. She is ordered to do so by Hera, Queen of the gods.
Hera! Now if we are talking evil, this might be a personification. She didn’t like her stepson Heracles. She stole his birthright (Pausanias 9.11. 3) and tossed snakes in crib (Pseudo-Apollodorus, Bibliotheca 2. 62) She made him mad several times. She created the scenario where he had to perform his dangers and horrifying dozen labors of which Ovid calls (Heroides 9. 35) "The acts of (King) Eurystheus, the instrument of Hera's unjust wrath, and the long-continued anger of the goddess." Not to mention attacks by miscellaneous other monsters and violent storms. But as usual we can’t judge divine actions by human standards. This life of suffering and violence, particularly a couple of the Labors are the very things that insured Heracles unwilting glory (kleos) and eventually immorality. As a matter of fact his name Heracles = Hera kleos = the Glory of Hera. As a matter of fact "From the time he [Herakles] achieved immortality, Hera's enmity changed to friendship, he married her daughter Hebe." (Bibliotheca 2. 160)
Yes there are still some monsters left for other heroes to slay. There are petty tyrants and foreign invaders. There is even a witch of two. But there is no evil of cosmic consequence battling the inherent good of the world. There is no Satan.