Jace

Jace meets Clary outside Pandemonium, the two clash right away, and he takes her to the Institute and the City of Bones, where Clary gives up her own memories to save him from a demon. They grow close, until Valentine introduces himself as Jace's father and says Jace and Clary are siblings. With his family and friends under threat, Jace ends up going with Valentine at the end of S1.

Jace escapes Valentine but gets blamed for a werewolf's death and arrested. The Soul-Sword lays bare what he believes, and he's cleared after Valentine steals the sword. Valentine reveals he experimented on Jace in the womb.

Bit by bit, Jace learns he isn't Valentine's son: he's a Herondale. The Seelie Queen forces a kiss between him and Clary, ending her relationship with Simon. His grandmother, Imogen Herondale, puts him in charge of the Institute, and he and Clary finally get together.

Late in S2, Jace accidentally activates the Soul-Sword, and Valentine uses it to kill the Downworlders in the room. At Lake Lyn, Valentine kills Jace. Clary uses the angel Raziel's wish to bring him back, and the resurrection has consequences nobody saw coming.

Lilith possesses Jace and turns him into the Owl. With no memory of it, he commits crimes, including killing his grandmother, Imogen. Magnus frees him by giving up his own magic. When Clary gets away from Jonathan, the two reunite. Later, Jace uses the sword Glorious to break the bond between Clary and Jonathan.

He fights Lilith in Edom, and Isabelle destroys her with heavenly fire. After Clary loses her memories of the Shadow World, Jace carries on without her. A year later, at an art show, she sees him through his glamour and touches his runes.

In the 2013 movie, Jace (Jamie Campbell Bower) saves Clary from a demon and brings her to the Institute. They kiss, which hurts Simon. Valentine says Jace is his son, which would make him Clary's brother. At the end, Jace tells her he needs her, that he doesn't believe they're siblings and that he'll find out the truth.

In the books, Jace is 17 and goes through more than one last name over the series. Dominic Sherwood plays him on the show; Jamie Campbell Bower played him in the movie.