“He’s actually pretty intelligent, but he acts so dumb sometimes. I wonder if he does it just to annoy me. The guy has a lot going for him. He’s courageous. He’s got a sense of humor.”

Percy is a brave, spirited natural leader, and is willing to risk his life to save friends, family, strangers, and sometimes even enemies. He has a sarcastic and smart sense of humor, a laid-back demeanor, and has earned the respect of all the Olympians, including Artemis (who strictly dislikes men), Dionysus (who hates most heroes because of what happened with Ariadne), and Hades (who generally hates demigods) and Zeus (who naturally hates children of Poseidon). He also earned the trust and respect of the Romans of Camp Jupiter (who usually don't trust Greeks). Percy remains true and never goes back on his word. However, he is definitely not perfect. Percy is somewhat short-tempered, and thus has trouble controlling his anger (such as when he sees bullying) and tends to do or blurt out things before thinking, no matter the consequences, causing him to get into a lot of trouble. He also feels responsible for everyone and anything which goes wrong. Percy is also really reckless and rebellious.

Many people tell him he is brave such as friends, family, strangers, and even gods and goddesses. He also states that he has the same "brooding" look as his father, that always branded him a rebel, and that his mom also has a rebellious streak just like him. Annabeth Chase mentions that he is technically smart but seems to act dumb; and is obtuse, meaning he doesn't always see the obvious even when it is right in front of him, such as people's feelings and what they are trying to see indirectly. Despite this he is perceptive when he wants to (or needs to) be; he could tell that Gaea wanted to keep him alive and gambled his life knowing that he was too valuable to Gaea for him to die at that time. Percy can also be derisively sarcastic and moody, and he dislikes being manipulated or forced to obey. Percy also has small feelings for Annabeth Chase at the beginning of the series and these feelings became romantic over the course of the series, but he finally confirms it in the The Last Olympian. Although Percy is a leader at Camp Half-Blood, he is considered a troublemaker in school, with a track record of expulsions, like most demigods. His dyslexia makes learning and reading difficult, and his ADHD makes it hard for him to be attentive or to sit still in class. He has never been one of the "cool" kids in class because he hangs out with supposedly "un-cool" people, such as Tyson or Grover Underwood. Possibly because of his bad history in school, Percy feels a strong level of affection and attachment to Camp Half-Blood.

Percy's fatal flaw is excessive personal loyalty: he would risk the world and even his own life to save a loved one or even a stranger according to Athena. Athena was obviously displeased that her own daughter is an object of that loyalty. Kronos previously exploited this trait in The Lightning Thief (Sally Jackson), The Sea of Monsters(Grover), and The Titan's Curse (Annabeth Chase). Athena also says "The most dangerous flaws are good in moderation" when Percy protests that personal loyalty isn't all that bad. .

Percy almost aways uses sarcasam amd jokes around. A big part of the time, he is just pesimistic, but he sounds funny and sarcastic. This is the main thing about Percy's voice i want to be known.