Lycaon

Lycaon was the first werewolf and a servant of the earth goddess Gaea.

History
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 assasins 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 wolfman 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.

The Lost Hero
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. 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 shows her true godly form.

Abilities
Being a lycanthrope, Lycaon is not only immortal, but also immune to any weapon that isn't made of silver, even magical ones like Imperial gold and Celestial bronze that's 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 isn't 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.

Trivia

 * It is unknown if Lycaon is immune to Stygian iron: a magical metal from the Underworld that can absorb a monster's essence.