Born and raised in Sparta, Castor is the twin brother of Pollux. Unlike his loud and boisterous brother, Castor is very calm and collected, preferring to talk things out rationally instead of solving problems with his fists. He is killed sometime between Winner Take All and Dad Always Liked Me Best, his death inspiring Pollux to change his brutish, arrogant ways.
- Parents: Zeus and Leda
- Uncles: Poseidon and Hades
- Immortal half-siblings: Aphrodite, Apollo, Ares, Artemis, Athena, Bacchus, Discord, Hephaestus, Hermes
- Half-mortal half-siblings: Hercules, Lucius
- Half-mortal siblings: Pollux
- Though Castor never showed himself to have any powers, it can be assumed that, like his brother and half-brothers, he likely had strength beyond that of a normal human's.
- A fast runner - 1.17 - Winner Take All.
- According to actual mythology, both Castor and his brother were excellent horsemen and hunters.