The main character - son of Poseidon, friend of Grover and Annabeth
A centaur - in the first part of the book, he was known as "Mr. Brunner".
A Latin Teacher - he works at Yancy Academy, and in most of the book he is known as "Chiron".
Percy's magical weapon, giving to him by his father. It looks like a ballpoint pen until you uncap it.
A Math Teacher - Worked at Yancy Academy and tried to kill Percy, afterwards he discovered that she is a Fury
Hades' revenge workers.
A huge, strong bull man - the first monster that Percy fights. This monster kills his mother.
Percy Jackson's mother - "the best people have the rottenest luck" is used to describe her life in the book. In the end she comes back to life and freezes Gabe with Medusa's head!! wooohooo!
God of the Sea - One of the Big Three, also Percy's father.
God of the Sky - Also one of the Big Three
God of the Underworld - One of the Big Three
The reason we have spring and summer - she goes to Hades for winter and autumn, and she comes up for spring and summer.
A monster that Percy meets in Denver in the form of a Chihuahua
"Aunty Em" - appeared as a nice Muslim lady wearing a head covering. She tried to change Annabeth, Percy, and Grover into statues with her eyes as she did many other people, but did not succeed.
A half blood - The daughter of a college professor and Athena
A satyr - is assigned to protect Percy at Yancy, and his ambition in life is to find Pan
The God of all things wild - disappeared years and years ago, and though many satyrs have gone to look for him, none have returned alive.
The God of Music
The Goddess of the Hunt
The Goddess of Wisdom
The Goddess of Love and Beauty
The God of War
The God of Wine - AKA "Mr. D."