[2][3]: 179  When Haley was in second grade and he was studying Greek mythology, he asked his father to tell him bedtime stories based on those myths.

This led Riordan to create the fictional character of Percy Jackson and the story of his travels across the United States to recover Zeus's lightning-bolt.

[4] Riordan received input on the manuscript from some of his middle school students before taking the idea of Percy Jackson to a publisher.

His personality is described as "changeable like the sea" and hard to predict — with the important exception that he is dangerously loyal to his friends and family.

[8] Percy's "powers", which start small and develop as the books proceed, include controlling water, making hurricanes, breathing underwater, and talking to horse-like animals and fish.

He arrives at a Roman establishment called Camp Jupiter, and is elected praetor as a result of the help he offers them on a quest.

He develops an irrational fear of drowning; is humbled by weakening sword-fighting skills; and expresses a new tendency to make ambiguous moral choices in defense of his friends and family.

One of the character's darkest moments comes in The House of Hades, when Percy discovers that he can control the water in a person's body, and uses it to torture the goddess Akhlys.

[11] At the end of The Blood of Olympus, Percy and Annabeth reveal plans to finish their senior year of high school together in New York, and then attend college in New Rome (a demigod-only city located in California, guarded by Camp Jupiter).

[11] In The Hidden Oracle, Percy has been accepted to the college with a full scholarship, provided he can pass his SATs and graduate on time despite the semester he spent away (while missing during The Lost Hero).

Between the time of The Battle of the Labyrinth and The Last Olympian, Sally marries Paul Blofis, a man she met in a writing seminar.

In The Hidden Oracle, Sally is seven months pregnant with Paul's child, and later gives birth to Estelle in The Tower of Nero, making her Percy's half-sister.

Though Percy is related to virtually every character and creature in Greek mythology through his father Poseidon, Tyson is one of the only beings whom he acknowledges as family.

Significant examples of this would be that he is technically a grandson of Kronos, nephew to Hades, Zeus, and numerous other Olympians, as well as the half-nephew of Chiron.

[13] Percy's oldest friend is Grover Underwood, a satyr originally tasked with protecting him and bringing him safely to Camp Half-Blood.

Percy also has a unique relationship with Clarisse La Rue, daughter of Ares and Camp Half-Blood's resident bully, whom he allegedly dislikes but often helps.

His brother Tyson and friend Charles Beckendorf are Mrs. O'Leary's other caretakers, though she is also fond of Nico di Angelo.

It first appears in The Sea of Monsters, where it helps Percy and his friends enter Luke Castellan's boat Princess Andromeda.

[10] Percy is described as handsome, with messy jet black hair, a Mediterranean[page needed] complexion, and sea-green eyes like his father Poseidon.

[15] Like most demigods, Percy has ADHD and dyslexia, the former because of his godly battle instincts, and the latter because his brain takes more naturally to Ancient Greek than to English.

After being trained at Camp Half-Blood, he has developed a Greek fighting style (described as unpredictable by New Romans) and is an expert swordsman.

[13][3][17] In The Sea of Monsters, his half-brother Tyson gives him a wristwatch that changes into a shield covered with designs, but the watch is damaged in The Titan's Curse and lost in The Battle of the Labyrinth.