His father fell in love with a woman who loved the sea and sea animals, she was a marine biologist. Poseidon eventually approached her and showed her cool sea things. They fell in love and they eventually had a kid(Caspian). But Zeus, being the way he is, killed Rose(his mom) because of the Oath of the Big Three. Poseidon didn't want the same to happen to Caspian so he raised Caspian underwater where he learned to love sea life and all those cool things. Caspian grew up as a shy child, he was easily frightened by small sea life, but he eventually grew to love them. Caspian was trained in camp Fish-Blood, so he's an extremely well fighter and baker. He was trained there be cause Poseidon wanted him to be his like, fighter person or underwater gladiator. Nevertheless, Caspian was interested in humans. He asked his father if he could go, his father originally intended to keep Caspian underwater so he could fight underwater. So he said no. And Caspian was all like angry and stuff so naturally he ran away. When he heard Percy came to Camp Fish-Blood, he learned about Camp Half-Blood and Camp Jupiter, and he was curious. So he decided to try to go to CHB.