Percy is a 12-year-old student from New York who struggles with dyslexia and ADHD. He frequently faces expulsion due to strange, unexplainable incidents around him. Fiercely protective of those he cares about, he possesses an instinctive ability to defend himself and a rebellious streak. His life shifts dramatically upon learning his true heritage, forcing him to adapt to a dangerous new reality.

Annabeth is a year-round resident at Camp Half-Blood and a daughter of Athena. She copes with a difficult family history by training vigorously and seeking opportunities to prove her worth. With storm-cloud-gray eyes and a tactical mind, she approaches problems analytically and dreams of becoming an architect to build structures that last.

Grover is a satyr serving as a keeper, tasked with protecting young demigods and escorting them to Camp Half-Blood. He appears as an overgrown middle schooler but hides his goat hooves under clothing. He holds nature in high regard, despises pollution, and aims to earn a searcher's license to find the missing god Pan.

Luke is the experienced counselor of Cabin 11, identifiable by a thick white scar running from his eye to his jaw. He holds bitterness toward his father and the gods for a past quest that left him feeling inadequate. Despite his resentment, he acts as a welcoming figure for new campers who do not yet know their divine parentage.

Operating under two identities, Mr. Brunner is Percy's favorite teacher at Yancy Academy, pushing him to excel in Latin. In reality, he is Chiron, an ancient centaur who serves as the activities director and protector of Camp Half-Blood. He holds deep wisdom and keeps crucial secrets regarding the prophecies surrounding the campers.

The god of war appears as a large, intimidating biker in black leather. He thrives on conflict and uses his brute strength to intimidate those around him. He involves himself in the demigods' journey by sending them on errands while harboring his own chaotic motives.

The god of the sea is one of the "Big Three" who swore an oath not to have more children after World War II. His decision to break this oath results in Percy's existence. He maintains a brooding demeanor and is currently locked in a bitter feud with his brother over a missing item of immense power.

Kronos is the ancient titan and father of the Olympian gods. Defeated millennia ago by his children, he remains imprisoned in Tartarus, the darkest part of the Underworld. Despite his confinement, he invades the dreams of mortals and gods to manipulate events on the surface.

Sally is a resilient and loving mother who stays in a difficult marriage to protect her son. She maintains an exuberant presence that brings comfort to Percy. Despite knowing the dangers her son faces, she tries to grant him moments of normal childhood joy.

The king of the gods and ruler of the sky. He is quick to anger and paranoid about losing his power. He accuses his brother of theft and threatens to plunge the world into a catastrophic war if his demands are not met by the summer solstice.

The god of the Underworld presides over the dead from his dark palace. He is bitter about his isolation from the other Olympians and is fiercely protective of his own territory and magical items. He relies on terrifying monsters like the Furies to enact his will on the surface.

Disguised as a strict pre-algebra teacher, Mrs. Dodds is actually a Fury, a loyal soldier of Hades. She targets Percy early in his realization of his powers, acting as the first true monster to penetrate the mortal disguise of his everyday life.

Percy's stepfather, nicknamed "Smelly Gabe" for his terrible odor and worse attitude. He is a loud, abusive man who spends his time gambling and bullying his family. His overwhelming human scent inadvertently serves a protective purpose for his stepson.

A daughter of Ares and the resident bully at Camp Half-Blood. She targets newcomers to establish dominance, relying on brute strength and intimidation. Her immediate clash with Percy sets the tone for his difficult integration into camp life.

A cursed figure from ancient myth living in the modern world under the guise of "Aunty Em." She creates lifelike stone statues, which are actually her petrified victims, and harbors a deep, ancient grudge against those connected to the sea and wisdom.

The ferryman of the River Styx, responsible for transporting the dead. He staffs the waiting room of the Underworld and demands payment in ancient drachmas. He is susceptible to flattery and cares deeply about his appearance.