|“||It was a question too elementary for any of the rest of them, but Tavvy looked pleased to be able to answer something.||”|
Tavvy was only two when he experienced his first war. He had been in the nursery when Sebastian Morgenstern and his Endarkened attacked the Institute in December 2007. Nonetheless, he had been aware of the chaos outside of the room as a child and was crying and screaming, with Dru protecting him determinedly with a sword she had yet to be trained to wield. Their family friend Emma Carstairs came to get them, and together, the three of them made it to the office in time and Portaled to Alicante with his siblings, with the exception of Mark, who had been captured by the faeries, and Helen, who was already in Alicante.
The children stayed with the Penhallows. He and Dru were haunted with nightmares following the raid. Because they were the first survivors of Sebastian's attacks on Institutes, his siblings and Emma were subjected to the Clave's interrogations using the Mortal Sword. Emma stated that the only reason Tavvy wasn't interrogated along with them was because he was still just a toddler, incapable of speaking.
Tavvy and his siblings went through a lot during the Dark War. During the final attack on Alicante, while the children hid in the Accords Hall, their father—revealed to have been Turned into an Dark Shadowhunter—arrived and attempted to take Ty, and presumably them afterwards. To protect them, Jules had to kill him. In addition, their brother Mark was left with the Wild Hunt, and their sister Helen was exiled to Wrangel Island. Because of the death of their father, a woman suggested that the children be taken to the Shadowhunter Academy or be split up among different Institutes. Fortunately, their uncle Arthur had already accepted the offer to run the Institute in his brother's place and to become the children's new legal guardian, allowing the siblings to stay together.
Arthur, however, had become unstable and became incapable of raising the children. They were instead cared for by their own brother Jules, as well as their new tutor, Diana Wrayburn.
Despite having been very young then, Tavvy became traumatized by the war. He was constantly plagued by nightmares, most of which relate to the war, and has since had trouble sleeping. Julian would sometimes sleep with him in the tent to sooth his fears. It also became a habit for the pair to go up to Julian's studio when something was frightening or bothering him as he found the room's elements soothing. Also since the war, it had become considerably difficult to get him to eat.
The age gap between him and his older siblings encouraged him to use his imagination to be able to entertain himself, and he was thus often content with playing by himself. Octavian learned to read when he was only four, and his shared love with his sister Dru—the one closest of age to him—strengthened their connection.
Along with his siblings, Tavvy visited their great-aunt Marjorie in 2012. While his siblings mostly suffered through the training, Tavvy was treated well and spoiled by their aunt. She gave him a Shadowhunter children's book, A Treasury of Tales for Nephilim, which he became attached to and would become the key to their later mission. They returned home in August, after two months in Sussex.
Tavvy helped his siblings in their investigation into the mysterious killings related to the murder of Emma's parents in 2007, eager to help in the small ways he could. It was Tavvy who, after hearing the older group's discussion and correlating it with a story he read from A Treasury of Tales, helped them figure out the rhyme written on the bodies they were investigating, giving them the key to understanding the mysterious murders.
At one point, while he and Dru were at the beach, Malcolm Fade—a trusted friend, and High Warlock of Los Angeles—came and told Dru that she was needed at the Institute and convinced her to leave Tavvy with him. Malcolm then took him to the convergence. While Tavvy slept, Malcolm was about to perform the ritual and take his blood—a sacrificial ritual that would have killed him—to resurrect his lost love, Lady Midnight when the others arrived and stopped him.
Tavvy shares the Blackthorn family's dark brown hair and blue-green eyes. According to Jules, he is quite small and thin for his age.
Following the family tradition of Greek and Latin names, Andrew named him Octavian after Gaius Octavius, who was adopted by Julius Caesar and became Augustus, the first emperor of Rome. It comes from the Latin word octavus, which means "eighth".
- Octavian was originally named Octavius, and was even once called the name in City of Heavenly Fire; whether this was a typo or a mistake on the character's part is unknown. He was also set to be around a year younger.
- Tavvy's room has a small bed, a big playhouse, and a tent that houses books and toys.