Valerus was one of the Argonauts who sailed with Jason to bring the Golden Fleece to Argos. Ten years later, he was part of the second expedition of the Argo when Castor and the Blood-Eye Cult stole the Fleece. Valerus was an expert archer but during the second expedition he was unable to fire even one arrow because he was killed by Castor during the quest.
Valerus did not appear in Young Hercules (film), and did not appear as one of the Argonauts; a possible explanation for this inconsistency could be that he was Liardus, and had changed his name to Valerus as he grew older.