User blog comment:Noctosphere/so? who's the first demon?/@comment-31564841-20160809120930/@comment-34326521-20160813070222

Two events: Lucifer being cast out of Heaven and Lucifer being put in the cage. Lucifer was cast out by Michael when he rebelled, and he was put in the cage by God after corrupting Lilith. However, it was never stated that he was immediately dumped in the cage after Lilith's corruption. I'm guessing there was some time before that during which Lucifer gave the Mark to Cain, to corrupt him too, and that's when God realized his mistake and punished Lucifer for it.