Lycanthropes, also known as werewolves, are humans that were cursed and have the ability to shapeshift into wolf-like creatures. The first Lycanthrope is Lycaon, their leader.
Description
Lycanthropes appear in many different cultures, more commonly known as werewolves, and they can only be killed by silver. In both myth and popular culture, there are many ways of becoming a werewolf, with the most well-known one (which is used in the series) being if an existing werewolf bites you.
In The Lost Hero, Piper described werewolves as being "black beasts bigger than Great Danes. Their fangs gleamed and their glowing red eyes looked intelligent."
History
In Greek mythology, Zeus invited Lycaon, the King of Arcadia, to dine with him. Lycaon wanted to know Zeus' real name. To prove that Zeus really was who he said he was, Lycaon tried to feed him human flesh. Then he hired assassins to attack Zeus while he slept to test the limits of his immortality. Zeus became so enraged he slew Lycaon's sons with lightning bolts and cursed Lycaon into being the first Lycanthrope.
Source: https://riordan.fandom.com/wiki/Lycanthrope#:~:text=Lycanthropoi%20