Jonathan Clark is the name of a decorated soldier serving overseas and the son of the old neighbors of Jocelyn and Clary Fray in East Village. He died when he crashed his car into a tree, supposedly just outside Albany.
Jocelyn led Clary to believe for years that Jonathan was her father and died before she was born, not wanting to tell Clary about Valentine, or to lie by telling her that her father left them. Because their neighbors had commissioned Jocelyn to paint a portrait of him in his Army uniform, Jocelyn kept his photo and had it framed and placed on their mantel. Coincidentally, he shared the initials of Jocelyn's son, providing an excuse for the box of his things with the initials "J.C." by her bed.
Jonathan is said to be a thoughtful-looking fair man, with laugh lines at the corner of his eyes.