Superman #51 1990

Superman #51 (DC, 2016) begins "The Final Days of Superman" arc, where the New 52 Man of Steel faces his impending death due to accumulated battle injuries. As his powers fail, Superman grapples with his mortality and the future protection of Earth. This issue is highly notable to collectors as it sets the stage for the demise of the New 52 Superman and the subsequent transition to the Rebirth era, paving the way for the classic Superman's return. It also introduces a new, powerful being claiming to be Superman.