Sydonai is the name of an Elder Demon, presumably a Eldest described in The Origin of Evil. He is one of the leaders of the demonic invasion of Earth. Sydonai is the Cthulhu-like squid monster depicted upon the Hellgate: London box art.
Flagship Studios writer Ivan Sulic describes Sydonai in the following terms:
- "Those are real names of Demons from various religions and mythologies and whatnot. Some are also real names locals have given to Demons. A lot of those are actually the same character, though. For instance, Æshma-deva and Asmodeus are the same creature. He goes by many names and is often referred to as the Lord of Lust. I have him in the game as Sydonai, an Elder Demon. Other names he has gone by include: Asmodai, Ashmadia, Ashmedai, Sydonaios, Asmoday, Asmodée, Asmodee, Asmodei, Asmodeios, Asmodeo, Asmodeius, Asmodi, Chammaday, Chashmodai, and Sidonay. I personally think Æshma-deva is the best alias of the lot, but it seemed a little too complex for the masses to grasp."
Sydonai is also the final boss of the game.