Not to be confused with Despereaux, the fictional mouse in The Tale of Despereaux. Despero attacks the League at their headquarters, and kills the comatose Steel on life support for injuries sustained during a battle against the androids of Professor Ivo. The arguing is stopped by a single gunshot.
The makers of the movie are so confident about it that there's a sequel in the works, as well as solo movies featuring Cyborg and Aquaman, sequels to Wonder Woman and Suicide Squad, and a spin-off called Justice League Dark, about a gang of deathy, grim, kind of monstrous superheroes! And on the way back to Earth with Simon Baz, she told him about it.