Jonathan "Jace" Herondale is a Shadowhunter living at the New York Institute with his adopted family. Jace's legal name changes throughout the series, from Jace Wayland (when his father is thought to be Michael Wayland), to Jonathan Morgenstern (Valentine's son), to Jace Herondale (When his true father is revealed to be Stephen Herondale). His mother was the young Celiné, a member of Valentine's inner circle with Stephen Herondale.
The nickname "Jace" was given to him by Maryse Lightwood after his (fake) initials J.C (Jonathan Christopher, because no one but Valentine knew Jace was not his real son), when he first began living with Maryse Lightwood and her family, because of his dislike for his name. Jace was given the blood of an angel by Valentine when Celiné was pregnant with him. This gave him enhanced abilities, even compared to regular Shadowhunters (Shadowhunters hunt demons that come into this world through portals from their own worlds), such as the ability to jump from extreme heights and survive, run faster than any other Shadowhunter, and the ability to move with a stealth close to that of the Silent Brothers (A group of Shadowhunters that have chosen not to hunt demons as is the typical Shadowhunter way of life, but to live secluded and gain knowledge. In that way they are similar to monks.)
For most of the books Jace's sarcastic, cold remarks and behavior hides his tortured and angry soul. In City of Ashes his strong "bad-boy" personality makes Maryse Lightwood (his adopted mother) somewhat scared of him, worried that he is too much like Valentine, whom was believed to be his real father until the assumption was proven false in City of Glass. Jace and Clary fall in love in City of Bones, making Clary the only girl Jace has developed real genuine feelings for, but after they find out they are "siblings," they encounter rather awkward situations throughout the series, and each of them attempting to get over each other by dating other people. He tries to avoid Clary and act as a real brother should act, acting slightly more joking carefree to her to mask how he really feels. He cannot control his charade all the time and is naturally overprotective and caring for her, although Clary does not see this due to her internal suffering. At the end of the third novel, City of Glass, Jocelyn contradicts Valentine's avowal that Jace and Clary are siblings, telling Clary that Jace is actually the son of Celine and Stephen Herondale. The truth frees Jace and Clary from the torture of having seemingly incestuous feelings for each other, allowing them to accept their mutual feelings and become a "real" couple.
Read more about this topic: List Of The Mortal Instruments Characters
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