Percy Jackson
Percy Jackson is the son of Poseidon, called Neptune in The Heroes of Olympus series. He is a troubled twelve-year-old boy with dyslexia and ADHD. After finding his new home, Camp Half-Blood, he gets a new girlfriend, Annabeth Grace another Greek demigod, a daughter of Athena. He has a very had life. One day he gets his memory whipped out and the only thing he can remember is a name: Annabeth. But he also ends up in a Roman demigod camp. Soon he finds out he is and how Hera had whipped his memory to try and get the Romans and Greeks together. Eventually he meets up with Annabeth and starts a new mission together to find a way out of Tartrus and seal the Doors of Death.
Jason Grace
Jason Grace is a son of Zeus, called Jupiter when in Roman form. He was switched with Percy in the trade that Hera had set up. Jason wakes up to not remembering anything, even his age, so he guesses he is a 15 or 16 year-old boy suffering from amnesia. He meets Piper McLean, who claims to be his girlfriend, and Leo Valdez, who claims to be his best friend, on a school bus ride to the Grand Canyon. He soon finds out he can fly and gets taken by Annabeth to Camp Half-Blood for questioning because Percy had been missing and the prophecy says that Jason will lead the Greeks to Percy. Eventually they find out what happened and get on the Argo 2 and fly to Rome to pick up Percy and the other heroes in the prophecy.
Leo Valdez
Leo Valdez is a son of Hephaestus, Jason's best friend, a kid with amazing talents. Leo exploring with Jason gets taken to Camp Half-Blood with Jason and Piper to find out he was a demigod, a kid who's father or mother was a god. His dad was Hephaestus and his mother..... his mother had died because of Gaea, Mother Earth. And soon finds out he has the talent to cast fire out of his bare hands, a gift from Hephaestus which has not been seen for a long time. And not only that he finds a gigantic dragon missing a couple parts and using his talents fixes the dragon and named it Festus. Festus eventually got blown into pieces on one of the missions but Leo kept the head so he could put in on the Argo 2. He has always felt like he wasn't important but he's a really important character in the story and they would have never been as successful at building defenses and other needs.
Frank Zhang
Frank is a big guy but he is a very soft-heated man. A while after Percy arrives at the camp Mars is revealed as his godly parent, although he was wishing Apollo would be his father. It is revealed later in the book that he has the ability to shape shift, he can change into any animal.This ability is inherited from his mother's side of his family. His life is linked to a stick of wood, which when completely burnt up, would end Frank's life as well. Frank is the only known demigod to be descended from a Greek and a Roman god, Poseidon on his mother's side and Mars as his father. Sadly, his mother was killed in Afghanistan at war.He has a secret crush on Hazel and envy's the fact that Hazel pays attention to Leo more.
Nico di Angelo
Nico di Angelo is a 12 year-old demigod, the only known son of Hades and the younger brother of Bianca di Angelo. Nico's Roman half-sister is Hazel Levesque, a daughter of Hades' Roman counterpart, Pluto. He has a weird aura around him tha makes everything seem like death. He is very gray but very thoughtful and smart and making decisions and what to do. He is always prepared like he had been when he got captured by giants. He had been searching for the Doors of Death so he could try and seal them so Gaea's army doesn't get raised from the dead. He was born around World War 2 and was put in the Lotus Hotel, a casino in which you don't age. And his knowledge about everything is great and useful in their expedition.
Hazel Levesque
Hazel Levesque, A demigod daughter of Pluto, she resides at Camp Jupiter, a secret camp built to train Roman demigods. She was brought to Camp Jupiter by her half-brother Nico di Angelo. She was rescued from the Underworld by Nico di Angelo.She was born in or around 1929 and lived in New Orleans. Her mother was a woman named Queen Marie, a mortal, who summoned Pluto during a spirit ritual. Queen Marie's relationship with Pluto resulted in Hazel. Pluto granted Marie one wish, and she asked for all the riches of the earth. Pluto warned that the greatest wishes would be the worst curses but Marie ignored this. When Hazel was born, she had the ability to summon precious metals and gems from underground. People see this ability as a curse, as anyone who has possession of the gems or metals dies or gets seriously hurt not long after gaining possession of them. On Hazel's thirteenth birthday, Gaea appears in another of Queen Marie's spirit rituals, and uses Queen Marie's resentment of Pluto for giving her a "cursed child" to persuade her to leave New Orleans and come to Alaska, the land beyond the gods, where Gaea tricks Hazel into raising Alcyoneus, using diamonds as his heart, and petroleum as his blood. Hazel dies in 1942 while preventing Alcyoneus from rising.
Annabeth Chase
Annabeth Chase is the daughter of Athena. Annabeth is considered to be very pretty, especially by Percy. Aphrodite once complimented her, saying, "Annabeth, you've grown into quite a beautiful young lady." Despite having good looks, she prides herself more on her intelligence and talent at fighting. As a daughter of Athena, Annabeth excels at anything having to do with academic studies or useful arts and crafts. One of her main weapons is her intellectual abilities, especially her strategic excellence.She is said to want to become an architect when she grows up. She is also a very powerful and experienced fighter, partially since she has been training since age seven. After a couple weeks of dating Percy he goes missing. She eventually finds him and goes on her solo quest to avenge the wrath of Athena.
Piper McLean
Piper is the demigod daughter of Aphrodite and Tristan McLean, a famous movie star of Cherokee descent. Resentful of her father's busy filming schedule, Piper steals to gain his attention. She steals all kinds of expensive items from stores, including jewelry. This often gets her in trouble, and makes her father upset with her. Shes been kicked out of 5 different schools. Soon after she steals a car, Piper is sent to the Wilderness School. Piper conceals her famous father's identity from others around her except her close friends. Her boyfriend is Jason is feels jealous when Reyna because she feels as if she is better. She also has a special knife in which if she looks at the knife will show her the future and what to do.
Arachne
Arachne was a great mortal weaver who boasted that her skill was greater than that of Athena, goddess of wisdom, weaving, and strategy. Arachne refused to acknowledge that her knowledge came, in part at least, from the goddess. Offended by Arachne's arrogance, Athena set a contest between the two weavers. According to myths the goddess was so envious of the magnificent tapestry and the mortal weaver's success, and perhaps offended by the girl's choice of subjects (the loves and transgressions of the gods), that she destroyed the tapestry and loom and slashed the girl's face. In another myth it is said that Arachne lost the competition, hung herself, and Athena brought her back as a spider. But Arachne has hated Athena and all her children from then on.