|“||Oh, we’ve been patrolling for you all across the west, demigod, hoping we’d be the first to find you. The giant king will reward me well when he rises. I am Lycaon, king of the wolves. And my pack is hungry.||”|
Lycaon was once a human king of Arcadia, the son of Pelasgus and Meliboea. He tested Zeus, who was a guest, by serving him human meat, including meat from one of his own sons. He also ordered assassins to attack Zeus while he slept to test his immortality. Zeus became angry as a result of his actions. As punishment, he turned Lycaon into a wolf-man and killed all of his fifty sons with lightning bolts, except possibly Nyctimus, who was the slaughtered child. The Greeks named werewolves Lycanthropes after him, the first werewolf. It is hinted that Lupa has animosity towards him, since she is the mother of wolves.
For nearly a millennium, Lycaon remained immortal until he affiliated himself with Gaea, the goddess of Earth. He eventually encountered Jason Grace, Piper McLean, Leo Valdez, and Coach Hedge while they were searching for the home of Aeolus. He was ordered to kill them with the exception of Jason, whom he is ordered to kidnap under the request of Khione. Whilst preparing to attack Jason, Piper, Leo, and Coach Hedge, Jason attacks Lycaon but because Jason's sword is Imperial gold, the weapon does not even injure Lycaon but passes through him. He says that Imperial gold, Celestial bronze, and mortal steel cannot harm him. Piper then realizes that lycanthropes can be injured by silver and because Lycaon is the first lycanthrope, silver is the only thing that can harm him. When they realize that they have no silver, the Hunters of Artemis show up and attack Lycaon and his minions. He is injured by their silver arrows and so he flees. His wolves, however, appear at the Wolf House under the leadership of Khione, but they run away or are destroyed when Hera is released and transforms into her true godly form.
Lycaon is working for Orion. He tracks down Nico, Reyna, and Hedge in Evora, Portugal. Reyna pulls out a silver knife before Nico traps him and his wolves in bone. He breaks free a minute later and attacks Nico before he stabs him with Reyna's knife. His shadow is then used by the trio to shadow travel.
His hair was greasy and ragged, the color of fireplace soot, topped with a crown of what looked like finger bones. His robes were tattered fur—wolf, rabbit, raccoon, deer, and several others. The furs didn’t look cured, and from the smell, they weren’t very fresh. His frame was lithe and muscular, like a distance runner’s. He had pale skin that was pulled tight over his skull. His teeth were sharpened like fangs. His eyes glowed bright red like the wolves.
Being a lycanthrope, Lycaon is not only immortal, but also immune to any weapon that is not made of silver, even magical ones, like Imperial Gold and Celestial Bronze, that are usually capable to harm even gods. Also, being the first lycanthrope not only makes Lycaon the most powerful of his species, but also makes him the leader of them, a thing that might explain his rivalry with Lupa, the wolves' leader. However, Lycaon is not truly indestructible as (was cited before) he can easily be injured by silver, harmed by fire, and is susceptible to divine power. He also has great reflexes, being able to catch an arrow in mid-air.
- It is unknown if Lycaon is immune to Stygian iron, a magical metal from the Underworld that can absorb a monster's essence.
- His daughter Callisto was a hunter of Artemis, and turned into a bear by the goddess.