In December 2007, Jason was Turned into an Endarkened, though the circumstances are unknown.
His sister was at Alicante during Sebastian and his army's siege on the Adamant Citadel. The relatives of the Endarkened left behind were told that they could try to cure them if they can capture their Turned friends. His sister became hopeful that he could be saved and rushed to join the forces Portaling to the Citadel.
At the Citadel, Jace Herondale and Clary Fray spotted Jason and saw him stab and kill a man they had just met moments before. His sister saw him then and tried to plead to him, to no avail. He laughed at her hopeful words and as she approached, Jason, no longer consciously making decisions of his own volition, then proceeded to cut off his sister's head.
Jason was a thickset man with blond hair.
- City of Heavenly Fire (first and only appearance)