|“||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 that 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 Endarkened 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 soothe 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.
A few weeks later, Tavvy was told his brother Julian, along with Mark, Emma, and Cristina Rosales, had gone on a mission to the Shadowhunter Academy. Within a few days, he and his other siblings, as well as Kit Herondale and Diana, were forced to evacuate the Institute when Malcolm rose from the dead and came to attack the Institute, still looking for Blackthorn blood.
They Portaled to the London Institute, waiting for the Clave to take care of Malcolm. During their time there, Tavvy learned of his uncle's illness and that Julian and the others were actually in Faerie rescuing Kieran. At one of their meals, Tavvy was seemingly able to see Jessamine Lovelace—the resident ghost of the Institute—as others noticed him staring at the air beside him and giggling.
Julian returned later that same evening and Tavvy was ecstatic to see his brother and wouldn't let him go. Thusly he was very upset the following afternoon when Julian was getting ready to leave on yet another mission; he attempted to stow away in the trunk of the car with their luggage. He seemingly got over it later that evening when Magnus Bane arrived with his two children Max and Rafael, whom he quickly befriended. He later, not without protest, accompanied them and Alec Lightwood to Alicante to stay safe from the Riders of Mannan.
Tavvy was at the Inquisitor's house in Alicante playing with Max and Rafe when his sister, Livvy, was killed during the chaos in a Council meeting. When Mark and Helen came to get him after the meeting, and Mark not too gently delivered the news, Tavvy began to cry and lash out, to which his new friends came out to hug and comfort him. At the funeral, Tavvy was seen clinging to his siblings.
After the funeral, the group was to be sent home to Los Angeles with Helen and her wife, Aline Penhallow. However, yet again, Julian would stay behind with Emma and Diana. Back at the Institute, in his grief over Livvy and his upset over being separated from his father-figure, he was cold toward Helen, telling her he didn't know her so he didn't have to listen to her. He soon became more welcoming towards her after Aline yelled at them and after Helen had helped sooth one of his night terror episodes. He even assisted Helen and Aline in setting up for the Registry and explained their ruse to any confused Downworlders: that they were registering them with fake names so they could not be found but were still technically registered.
Following Julian's war council meeting, Tavvy was sent ahead to Idris with Dru, Max, Rafe, and Maryse Lightwood. They spent the night in the Graymark house and the next afternoon watched the Cohort's parley projection nearby. As the battle began and the projection went out, Dru told him to go inside with Maryse as she ran toward the gate. Tired of being left behind, Tavvy refused and followed her. Together they let the prisoners out and watched the battle from the gates. When they saw Julian and Emma rise up as True Nephilim, they marched onto the field with the rest of their siblings to try to talk them down. Tavvy approached them first, giving Drusilla the push she needed to begin speaking. Tavvy later, after everyone else had spoken, delivered the final blow that brought them down by asking Julian to carry him home.
In the coming weeks, Tavvy really grew to love, and enjoy spending time with, Helen and Aline: at Magnus and Alec's wedding, he was seen mostly playing or cuddling with them. Also by then, he was surprisingly okay with Julian leaving soon for his travel year.
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 set to be around a year younger, and his first name was Octavius. The name was used in early copies of City of Heavenly Fire and was corrected in later editions.
- Tavvy's room has a small bed, a big playhouse, and a tent that houses books and toys.
- Building sand castles bores him so he usually builds what he calls sand cities. These consist of rows of structures meant to be houses, stores, and schools and include signs made by torn-off fronts of matchbooks.