>>17793693
Related to your question, I have to go back to Euripides’ Electra. While Clytemnestra was their birth mother and the main antagonist on whom they seek revenge it is their stepfather Aegisthus who actually killed Agamemnon and who gets a more scathing death in comparison (Electra delivers a long soliloquy on Aegisthus’ death reprimanding him on his cowardly ways which in comparison, Clytemnestra herself doesn’t get anything similar).

https://m.youtube.com/watch?v=UI4FoDnpOsc&pp=ygUgRmVzdGl2YWwgb2YgYmFjY2h1cyBlbGVjdHJhIDE5NjLSBwkJwwkBhyohjO8%3D

I would consider Aegisthus the first example of the evil step parent archetype in fiction.