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. Loyal and Devoted
He's never known his father and struggles to make friends. Nevertheless, his troubled life doesn't affect his loyalty to his best friends Annabeth, Thalia and Grover or his devotion to his loving mother. Even when Percy faces temptation, he chooses loyalty over money, rewards and personal gain.