<P> Percy is the son of Poseidon; his mother, Sally Jackson, married a man named Gabe Ugliano when Percy was young . Ugliano was abusive towards Percy and Sally, the latter of whom leaves him in The Lightning Thief . </P> <P> Between the time of The Battle of the Labyrinth and The Last Olympian, Sally Jackson marries Paul Blofis, a man she met in a writing seminar . Percy likes and respects his new step - father and eventually reveals to him that he is a demigod . Though understandably shocked, Paul still stays with the Jackson family and accepts Percy's complicated life . In The Hidden Oracle, Percy's mother is seven months pregnant with Paul's child (Percy's half sister). </P> <P> Percy has a brother named Tyson, who is a cyclops . Though Percy is related to virtually every character and creature in Greek mythology through his father Poseidon, Tyson is one of the only beings whom he acknowledges as family . Percy first met Tyson at a school called Meriwether Prep, and did not learn of their relationship until much later . Percy is also distantly related to horses, pegasi, some other monsters, and numerous gods and demigods through his father . Significant examples of this would be that he is technically a grandson of Kronos, nephew to Hades, Zeus, and numerous other Olympians as well as the half - nephew of Chiron . </P> <P> Percy's oldest friend is Grover Underwood, a satyr originally tasked with protecting him and bringing him safely to Camp Half - Blood . His next - oldest friend is Annabeth Chase, whom he meets when she helps nurse him back to health after his first fight with the Minotaur . The two accompany him on his first, and most of his subsequent, quests . </P>

Is percy jackson the only son of poseidon