Geryon

The devil Geryon ruled the Fifth Layer of Baator for many centuries. At least until the Reckoning, where Geryon was the only Archduke to rise in the defense of Asmodeus. The reward for his loyalty was to be deposed and have Levistus reinstated (although never freed from his icy prison).

What happened to Geryon remained a bit of a mystery, though it is said that after the betrayal he began to doubt his actions and lost all hope at which point Asmodeus struck him down even further, obliterating him. Some believe that the energy was never transferred back to Levistus, since why would he need it if buried under a glacier of ice? The story goes that Levistus was being used as a novel distraction for the rest of the Archdukes and that Geryon's energy was being stored until Asmodeus' daughter Glasya was ready to be promoted to rulership over the Sixth layer.

As for Geryon himself, stripped of his power, what remained of his essence departed into that in-between space where Vestiges go, granting those who seek him out powerful vision bonuses and a gaze attack, though his influence is to force his binders into becoming overly trusting to the point of being dangerously naive.

...But then he somehow got better in 5e. Mordenkainen's Tome of Foes has a section on the Archdevil cults which notes that Geryon's consists of individuals with whom he strikes bargains. Those who seek brute strength like orcs, trolls and ogres are often drawn into the fold, and Geryon rewards them with the traits Crushing Blow and Indomitable Strength. This means that despite being deposed he still has some degree of power.

Gallery

• 
  1e
• 
  2e
• 
  5e