|“||Oooh, a Shadowhunter. Scary.||”|
In August of 2007, Jacob was among the vampires who attended Magnus Bane's party. He was among the vampires who made a scene at the party before leaving, as some of their motorcycles had been vandalized, and some of theirs, among them Gregor, were missing. He particularly complained that their motorbikes would take hours to fix. The group irritated Magnus with their complaining and promptly ended the party. Jacob, still by the door, stopped Clary Fray on her way out and asked what was inside the bag she was holding protectively. When Jace answered for her and told him it was holy water, Jacob realized that he was a Shadowhunter; he sarcastically feigned fear and left.
When a group of Shadowhunters came to the Hotel Dumort in search of their mundane friend Simon, who had been turned into a rat that Elliott had accidentally taken back with them from the party, Jacob was the first to heed their warning and acknowledge that they were Nephilim. He tried to restrain Lily during the negotiations, and was the one who pointed out that their hostage, Raphael, was their interim leader, much to Lily's disapproval. When Clary bargained Raphael's life for her friend, Jacob, not knowing about the rat, misunderstood and thought she meant a vampire. He then agreed with Lily that an oath sworn on their angel was necessary before they agreed.
During the fight that ensued, Jacob tried to restrain Clary, who had taken Simon before they could finish discussing their terms. To save her, Jace threw holy water at him. His fingers burned upon contact, and he was forced to release Clary. Lily later called out for him and came to help him.
A month after, Jacob was among the vampires who accompanied Raphael Santiago to Idris. When the vampires were bargaining their support for Nephilim in exchange for the Daylighter Simon, he was next to Raphael and Lily when Simon came to them. While Jacob did not recognize the Mark of Cain on his forehead, Raphael did, and, like the others, became anxious when Raphael himself showed fear. Later, when Simon explained that it wasn't Shadowhunter blood that made him a Daylighter, Jacob confirmed this, having known vampires who had drunk blood of Nephilim but did not become Daylighters.
Jacob is thin, has blond hair that he dyes a dark black, and has an earring in the shape of a stake on his left ear.