Friendship is a central theme in many of Rick Riordan's books. His characters often rely on their friends to help them through difficult situations. For example, in the Percy Jackson series, Percy, Annabeth, and Grover are always there for each other, even when they are facing dangerous enemies.
Courage
Courage is another important theme in Rick Riordan's books. His characters often have to face their fears and do what is right, even when it is difficult. For example, in the Heroes of Olympus series, Jason, Piper, and Leo must overcome their fears and work together to save the world from the evil Gaea.
Family
Family is also an important theme in Rick Riordan's books. His characters often have strong bonds with their families, even if they are not related by blood. For example, in the Kane Chronicles series, Carter and Sadie Kane are siblings who are very close to each other, even though they have different mothers.
Identity
Identity is another important theme in Rick Riordan's books. His characters often struggle with who they are and where they belong. For example, in the Magnus Chase series, Magnus Chase is a demigod who is trying to find his place in the world.
Diversity
Diversity is an important theme in Rick Riordan's books. His characters come from all different backgrounds, and they all have their own unique strengths and weaknesses. For example, in the Trials of Apollo series, Apollo is a god who is turned into a mortal, and he must learn to live among humans and accept their different ways of life.
Humor
Humor is also an important theme in Rick Riordan's books. His characters often make jokes and have fun, even in the midst of serious situations. For example, in the Percy Jackson series, Percy and his friends often make jokes to each other, even when they are fighting monsters.