The Amazing Spider-Man #512 (Marvel, 2004)

Spidey squares off against two masked foes on this cover for the fourth installment of the continuity-shattering storyline, "Sins Past." While these faceless enemies might appear to be generic baddies, they are in fact Gabriel and Sarah Stacy -- twins born from the genetic splicing of Norman Osborn and Gwen Stacy, created by Mendel Stromm. The twins had debuted just a few issues earlier in ASM #509, but this issue delivers the shocking reveal that Norman is their biological father -- a revelation that would rock Peter and Mary Jane's relationship and send lasting shockwaves through the Spider-Man mythos.
Though "Sins Past" remains one of the most divisive storylines in Spider-Man history due to its controversial treatment of Gwen Stacy's character, it is undeniably a pivotal moment in the modern era of the wall-crawler's legacy. This is a chance to own a powerful piece of that history, illustrated by the incredibly talented Mark Deodato Jr., who provided both cover and interior art for all six issues of the arc.