One of the most shocking events in DC history was the fall of Hal Jordan when he became the villain known as Parallax. The story was perhaps the height of '90s edgy story-telling and the natural conclusion to the decade of character deconstruction that came before. However, the cause of Jordan's fall to villainy was caused by the death of Superman in the titular story, and the events of the Man of Steel's return arc.
Source：https://www.cbr.com/return-of-superman-hal-jordan-parallax/
