Space Shocker are an organization comprised of revived kaijin seeking to control the entire universe and the main antagonists of the film Super Hero Taisen Z. Their named is based on Shocker, the terrorist organization which fought the original Kamen Riders.
Various past monsters and Shocker members are resurrected thanks to the power of magic and reunite once again under the flag of Shocker, although calling themselves "Space Shocker" and aiming to conquer the entire universe, not just Earth.
The man behind their resurrection was Reider from the Space Crime Syndicate Madou who was using Space Shocker as a mere cover up, and who had his own plans to rule the universe, using this new Shocker as a fighting force and distraction while his own plan wasn't completed.
This is in the same vein as Dai-Shocker, the alliance of villains from across the Kamen Rider Series multiverse who originally appeared in Kamen Rider Decade, and returned in the first Super Hero Taisen.