Grover Underwood

Grover is introduced to us as a normal human early on in the book, but he is soon discovered to be a satyr, who is tasked with protecting Percy. He is Percy's best friend and the two of them are joined by Annabeth who is the third companion on their quest to save his mother and inadvertently return the master bolt to Zeus. He is the first to realize that they had stumbled onto the lair of Medusa when he sees his uncle Ferdinand as a stone statue and recalls how he had died.