Most comic book adaptations get made as planned, go on to make millions and introduce classic heroes and villains to a new generation of fans. Others endure a troubled journey to the screen, and some never even make it before the cameras.
More than a handful of superhero films, some more promising than others, have been announced and assigned to a director, only to be cancelled before taking shape.
Fan just love to speculate about how these movies might have turned out. A select few could have been classics, while others would probably have set comic book adaptations back even further than Batman & Robin.
Sometimes scripts from these projects turn up online, but often the only hints about how they might have shaped up come from concept art the studio released to drum up hype, or the designs that were leaked long after the plans turned to dust.
There's a mountain of old concept art out there, giving fans a glimpse at the superhero movies that only happened in a parallel universe, and here are some of the most striking sketches and illustrations...