He was the son of the previous Prefect-King and, in 2268, he was arranged to be married to Dohlman Elaan of Elas as part of peace negotiations between their two worlds. Upon their marriage, Cosalthan became Prefect-King, and he and Elaan went on to jointly rule both their worlds. (FASA RPG module: The Federation; FASA RPG - The Orions module: Book of Common Knowledge)
- The FASA RPG's The Federation has Elaan marry "the son of Troyius's current ruler", while The Orions: Book of Common Knowledge says she married "the Prefect-King of Troyius, Cosalthan II", suggesting that he ascended to Prefect-King shortly before, during or after his marriage. The TOS novel: Firestorm states that Elaan's husband was named Bejas and was the leader of Troyius.