Kronos is a character from Rick Riordan's book Percy Jackson and the Olympians: The Lightning Thief. Kronos is a bit of a character oddity, though, in that readers never actually get to see him; however, he still plays an important role in the story. He is the character who lures Percy down into the Underworld, and Kronos does this by speaking to Percy through dreams. Kronos is what is known as a "Titan," and as a Titan, he cannot die. This is an important detail because Kronos has been cast into the pit of Tartarus in a thousand pieces, yet he is not dead. Additionally, Percy suspects that Kronos is heading up a plot to overthrow and destroy the Olympians; however, Percy has a difficult time of convincing Zeus of this fact.

"In the First War, Percy, Zeus cut our father into a thousand pieces, just as Kronos had done to his own father, Ouranos. Zeus cast Kronos's remains into the darkest pit of Tartarus. The Titan army was scattered, their mountain fortress on Etna destroyed, their mountainous allies driven to the farthest corners of the earth. And yet, Titans cannot die, any more than we gods can. Whatever is left of Kronos is still alive in some hideous way, still conscious in his eternal pain, still hungering for power."