Hercules

Hercules had extraodinary strength and courage, but was not particularly intelligent. He acts without thinking and is prone to fits of rage which usually end in death for his opponent. He wears a lion skin (made from a Nemean lion) often accompanied with a club. Hercules was an extremely passionate and emotional individual. He will also go to great lengths to help his friends. Hercules was very much hated by Hera, the wife of Zeus, because he was Zeus's son. Hera tried to kill him many times, from the time of his birth to the time of his 'death' as a mortal.

One of the things he is most known for are the twelve labors he had to complete. These were a series of tests and well "labors" that were given to him to purify him after he went mad and murdered his wife and son.

The series
Hercules is mentioned, and Percy dreams from his point of view. Zoë Nightshade was the one who gave him the ideas for several of his labors, including how to steal the Apples of the Hesperides. Hercules, however, never even mentioned her. Percy used to think of Hercules as his favorite hero, because he had such "rotten luck" and it made Percy feel better about his own plight. Once he learns how Hercules treated his friend, however, he changes his mind. Percy's sword, Anaklusmos, was originally owned by Hercules.

Trivia
His name in Greek is Heracles. Hercules is the Roman spelling.