R'lyeh

R'lyeh ("Titan") was a tool which the Lizard Kings genetically engineered to shape the land on Mondas. The creature, however, was insatiable and continued to grow and consume. Before it could devour the whole planet, the Lizard Kings imprisoned it in a cage of living protoplasm and buried it deep beneath the ground.

When the Cybermen began to build a great city in the south, their digging released the creature. It quickly took control of their Saurian mounts, which turned on and devoured many Cybermen. Energy weapon fire trained on the monster was absorbed. The Cybermen finally contained it by electrifying the stromata of the protoplasmic prison. (COMIC: The Flesh Unbound)

The Necronomicon contained a reference to something called R'lyeh in a passage in an unknown language. (PROSE: The Banquo Legacy)

Behind the scenes

 * was the name of the sunken city Cthulhu was entombed in in H. P. Lovecraft's story "The Call of Cthulhu". The passage which The Banquo Legacy ascribes to the Necronomicon comes from the same story.