Duke Sucellus was the commander of the Sixth Legion in the army of Zaros, and one of the twelve Chthoniandukes given to Zaros by Hostilius. In the damaged digsite letter, he is referred to as Duke Sucellus, Father of Abominations and is noted as still alive during the time the letter was written.
Duke Sucellus appears in Children of Mah, during Kharshai's memories of the betrayal of Zaros. The duke seems more preoccupied with eating the citizens of Senntisten than anything else until Zamorak arrives with his allies, at which point the duke fights against Lowerniel Drakan.
Sucellus features in Mod Jack's comic The Empty Throne as being present during Zamorak's betrayal. He is depicted as a large, tentacled creature with many eyeballs and mouths.