When Sebastian Clark was a child, his father wrote a tell all book on the Court of Owls called "The Secret History of the Court of Owls." No major publisher would touch the book, and when a small publishing company agreed to publish the book, the Court of Owls assassinated all that had even heard of the book, including Sebastian's father. Sebastian himself managed to escape the Court, and fled to Europe. Unable to live his life in fear, he dedicated himself to learning all he could about the Court of Owls, in an effort to find a way to destroy them once and for all. It wasn't until many years later, after The Night of the Owls, where Sebastian came across Calvin Rose, the only person to escape the fate of being one of The Talons, and finally found the opportunity to destroy the Court he had been searching for.
It is revealed in Talon #6 - Grandmaster that Clark was the former Grandmaster of the Court of Owls. After leading the failed attack in Batman in Batman: The City of Owls, Clark was deemed unfit for the Grandmaster role by the Court. Before he could be removed, however, he vanished. It is after this when Sebastian seeks out Talon and recruits him.
Sebastian Clark was created by Talon writers James Tynion IV and Scott Snyder.
Major Story Arcs
Meeting Calvin Rose
Shortly after The Night of the Owls, where Batman and his allies delivered a serious blow to the Court of Owls' numbers, Calvin Rose catches wind of the apparent fall of his former masters, and returns to Gotham City to see for himself. In the process of his investigation, Calvin trips an alarm, that not only alerts Sebastian to his presence, but an escaped Talon as well. After Calvin barely defeats the Talon, Sebastian finds him wounded in the Metropolitan Terminal and pours liquid nitrogen on the defeated Talon to avoid her from coming back to life, and nurses him back to health in his compound. Once Calvin wakes up, Sebastian tells him of his story, and despite initial hesitation, manages to convince Calvin to work with him, in his quest to destroy the Court.