Percy Jackson
He always tells horses, which his father is said to have created, not to call him "boss" or "lord" whenever they talk to him but does not get annoyed when Annabeth calls him "seaweed-brain". His fatal flaw is loyalty.  Percy, like most boys his age, has trouble talking to girls. Athena said that Percy's fatal flaw is personal loyalty. He will do anything to save his friends and loved ones. Kronos uses this flaw to control him several times in the series, such as when his mother is held hostage when Grover is trapped on Polyphemus' island, and when Annabeth is kidnapped.