Born into the Starkweather family, Aloysius grew up in the York Institute, the Institute having been run by his family for generations. Raised during the days when there was still no peace terms between Shadowhunters and Downworlders, Aloysius despised them, seeing them as inferior beings not deserving any rights of any kind.
When he was around twenty-six years old, Aloysius was part of the Enclave group that was dispatched to kill John and Anne Shade for the illegal possession of the Book of the White and the practice of necromancy, a violation of Nephilim Law. Aloysius relished in what he considered the "glory" of slaughtering Downworlders and getting spoils from them.
Eventually, after years of aiding his father in his Institute responsibilities, Aloysius' father died at 104 years old. At some point before or after his father's death, Aloysius was left with the Institute and became its head.
Some time then, Aloysius's son had a daughter named Adele, a healthy child who was one day secretly switched by faeries with a sickly mundane child as a form of revenge against his cruel ways. Aloysius became particularly attached to Adele, and Adele trusted and loved him despite his gruff demeanor that usually bothered others. No one in the family, save the child's mother, noticed the switch. When "Adele" was ten years old and set to get her first runes, her nature as a mundane was revealed when she went insane and died, prompting Aloysius' son and daughter-in-law to move to Idris. The shock also apparently killed his wife. Heartbroken and lonely, Aloysius has since been interrogating demons and Downworlders alike, trying to find out what happened to his granddaughter, to no avail.
By the 1850s, the Clave had begun considering the peace treaty between Shadowhunters and Downworlders which soon became known as the Accords. Aloysius was among those who drafted the terms of the Nephilim in the attempts to form an agreement, though he was not entirely on board.
For a long time, Aloysius was friends with Granville Fairchild. However, they once had a massive argument and the two never spoke to each other again. Aloysius then took the grudge he held towards Granville and focused it on his daughter, Charlotte.
At 89 years old, Aloysius was still running the York Institute and, because of the generations of Starkweathers who'd been involved with the Institute, Aloysius treated and had the Institute decorated like a family home.
During an investigation by the London Institute into Axel Mortmain's past, they uncovered a case filed by Mortmain through the York Institute to recompense the death of his parents. Being their only lead, Charlotte was forced to write to Aloysius asking for assistance. Still bitter because of his rift with Charlotte's father, he declined, but Charlotte insisted on letting Will Herondale, Jem Carstairs, and Tessa Gray proceed to the York Institute to personally obtain the files.
Aloysius intended to send them away as soon as they arrived. Upon seeing Tessa, who resembled his daughter-in-law, Aloysius changed his mind and let them stay. Over dinner, he retrieved the files and discussed it with them. He then showed them the spoils he had gathered over the years from killing demons and Downworlders. He let them stay the night when Tessa collapsed upon seeing his spoils. The next day, he sent them on their way.
Unbeknownst to him, Tessa Changed into him for their investigation on Mortmain using a button that had fallen from his coat's cuff. Tessa noticed that his mind and memories were already fragmented—that he was already becoming too senile with age.
Aloysius also attended the Council meeting where the Magister issue, as well as the leadership of the London Institute and Enclave, was discussed. Mortmain's clockwork machines came, and before he left, he went up to Tessa to ask her if she was okay.
At one point, Aloysius finally discovered the truth about Adele when he returned to interrogating faeries for information about his granddaughter. Eventually, he tortured enough out of Sallows: he was told that Adele was switched with a mundane child for revenge. He was able to trace his granddaughter and eventually realized that Tessa's mother was his long-lost granddaughter, making Tessa his great-granddaughter and, thus, part-Shadowhunter. He also learned that Tessa was "the key" to the Magister's plans.
Overcome by concern for his missing kin, he approached Charlotte Branwell and told her his newly-discovered information, hoping that she could help her on his behalf, knowing that the Clave would not listen to him. He then asked her to tell Tessa that she would be welcome to take on the Starkweather name.
During the emergency Clave meeting called by Consul Wayland, Aloysius spoke in defense of Charlotte. When the automatons came soon after and beheaded the Consul, he reiterated his finally proven point: that they should have listened to Charlotte. Before he could finish his statement, he was subsequently slain by an automaton and was lifted off the ground by his throat. It would only be after his death that Tessa learned of their connection.
Aloysius was a rude and ill-tempered man, whose attitude carried onto his adulthood and later years, making everyone see him as a senile and grumpy old man.
Raised not to see Downworlders as people or beings worthy of value given to humans, Aloysius had a personal hatred of them that only worsened over the years. Aside from that, he was considerably sadistic and cruel towards them, taking pride in all the pain, suffering, and death he brought upon them in his life. Proud and forceful, Aloysius was a traditionalist, particularly unwilling to agree and conform with the Accords and all the terms, such as the Reparations, that gave them rights; he was often heard reminiscing about the times when they could kill Downworlders for little to no reason, a practice he was an active participator of. He also refused to see or acknowledge that humans were just as capable of the evils he always associated with Downworlders and that the latter were not all evil and also capable of kindness if shown the same.
Aloysius, at almost 90 years of age, had a wrinkled face as well as a beard and hair that had turned white with age. He had dark, gray-black eyes. Aloysius often wore a look of contempt on his face, though he can also sometimes look kind and sharp when not contorting his face.
- Vampires, Scones, and Edmund Herondale
- Clockwork Prince (first appearance)
- Clockwork Princess
- The Wicked Ones (mentioned only)
- The Last Stand of the New York Institute (mentioned only)
- Aloysius shares the name with Jocelyn Fairchild's grandfather, Aloysius Fairchild, whose son also shares a name with his old friend Granville. His own granddaughter Adele also shares a name with the mother and daughter of Jocelyn.