William "Will" Owen Herondale (1861-1937) is the middle child and only son of Edmund and Linette Herondale, the younger brother of the late Ella, the older brother of Cecily and a love interest a later husband of Tessa Gray in the book series The Infernal Devices by Cassandra Clare.
Will was born in Wales in 1861 as the second child and only son of former Shadowhunter Edmund and his Mundane wife Linette who already had a daughter named Ella and later had another daughter named Cecily. Despite Edmund leaving The Clave, Will along with his sisters were asked to become Shadowhunters but they turned this down as they were raised to believe that Shadowhunters where monstrous. When he was twelve, Will was looking through his father's old Shadowhunter things and came across a Pyxis and accidentally freed Marbas, the demon trapped inside it. Ella came to protect Will but got attacked by Matbas who then placed a curse on Will saying that anyone who loves him will die. The next day, Ella died from her injuries, but Will believed this was because of the curse and run away from him to protect his family and went to The London Institute to be a Shadowhunter.
During his time there, Will acted distant to the other residents of the Institute to stop them caring for him, fearing they would die. Sometime after arriving, Will attended a Christmas Party at the Institute where he found a diary which belonged to a twelve year old Shadowhunter named Tatiana Lightwood who had a crush on him. In the diary, Will found poems Tatiana wrote about him and wrote her name as Tatiana Herondale. Still believing in the curse, Will decided to put a stop to Tatiana's crush on him by reading out the poems in front of the entire London Enclave. Will succeeded in ending Tatiana's crush on him, only to be attacked by her older brother Gabriel. Will ended up breaking Gabriel's arm and since then the two boys have never got along. The only one he showed kindness to was his parabatai Jem Carstairs (who was slowing dying from affects from a demon drug). In 1878, Will (now 17) rescued a 16-year-old American half Demon/half Shadowhunter girl named Tessa Gray from The Dark Sisters but like others acted distant towards her. However, later that year, he encountered Marbas again and discovered that the demon didn't curse him at all and that Ella had died from her injuries. After hearing this Will confesses his feelings for Tessa but couldn't pursue a relationship with her due to Tessa being engaged to Jem. However, after Jem became a Silent Brother to stop dying from the drug, Will and Tessa started a relationship and at a Christmas party, Will proposed to Tessa which she accepted. Will along with Tessa and his remaining sister Cecily reunited with his parents and introduces Tessa as his fiancée to them.
Will and Tessa eventually married and had two children together, a son James and a daughter Lucie. Will died in 1937 aged 76 surrounded by Tessa, Jem (now known as Brother Zachariah) and his friends and family. In 2009, Will's ghost witnessed the wedding of Tessa and Jem at Blackfriars Bridge.