Thesily had a great passion for the people of Atlantis, but his policies and ego often came into conflict with that of another former Atlantean monarch - Aquaman. Thesily's attempts at diplomacy were often misguided, and he all but blamed Aquaman for the devastation that struck the capital city of Poseidonis during the Oumland affair. In fact, it was actually King Thesily who attacked Oumland over a minor border dispute, which perpetuated the latter's attack against the undersea kingdom. As this flareup evolved into an international incident, Thesily appointed Minister F'ancha to serve as Atlantis' liaison to the United Nations.

A short time later, Thesily was present in the Atlantean Royal Palace when the entire continent began to slowly rise out of the sea. The ensuing quakes caused massive collateral damage and Thesily was killed when a piece of debris fell on top of him.