Nhehnen (stygian) was part of the Academy and invented an advance version of academy fire (which is a substance for flamethrowing, that ignites with contact with water)
They were removed from the Academy as this was too dangerous, and sent to the Isle of Exiles. Admiral Fabien Gold welcomed them as a member of the Saviour of the Seas.
While travelling with the Navy, they used the Academy Fire in battles and takeovers, however never told anyone the secrets. While part of the Navy, they travelled with Xanthia Ornis (Arkelander) for a while so are familiar with her relationship with Gold, and refer to her as 'his protege'. During their time together Xan and Nhehnen had a mutual respect for each other, as a neighbour may have for a child in their neighbourhood.
When Civil War broke loose on the island, they isolated themselves to protect the secret of their advanced academy fire. Either of the parties having this secret would guarantee many deaths.
Note: their hair is greying but this was hard to do in an image so you have to imagine it.