Disappointed by Shocker's numerous failures to defeat Kamen Riders Ichigo and Nigo, the Great Leader of Shocker, secretly met with General Black, an executive of the mysterious Geldam organization from America, to discuss the merging of their two organizations. They eventually put their plans into action after the death of Ambassador Hell.
As part of their agreement and seeing that the other leaders of Shocker were unfit to join the new group, Great Leader of Gel-Shocker ordered the deaths of nearly all of the lower members of Shocker. The Great Leader had all former Shocker personnel purged, blowing up various remaining Shocker secret bases worldwide and having all of the Shocker Combatmen liquidated and replaced with Gel-Shocker Combatmen. Black sent the Geldam kaijin Ganikomol to exterminate the remainder of the Shocker Combatmen so they could be replaced with stronger Gel-Shocker Combatmen. Ganikomol was later encountered and defeated by Kamen Rider 1. Although Rider 1 destroyed Ganikomol he was unable to prevent the merger of Shocker and Geldam.
Rising from ashes of Shocker came Gel-Shocker. Despite being led by the Great Leader of Shocker, the majority of the organization's resources were provided by Geldam, with the Shocker Riders being the only visible carryover from Shocker. And when Gel-Shocker was ultimately destroyed, Geldam went down with it.