Castor of Argos was a famed Argonaut, noted for his acrobatic skill. He attempted to become the king of Argos. (HTLJ: "Once a Hero") Castor was amongst the crew of the Argo when the Golden Fleece was found, although he didn't meet Hercules until after the voyage. (HTLJ: "Once a Hero", YH: "Winner Take All")