In the first game of the Sly Cooper franchise, what family heirloom did Sly Cooper want to steal back?

In the first game of the Sly Cooper franchise, Sly Cooper wanted to steal back the family heirloom known as the Thievius Raccoonus. This ancient book held the secrets and techniques of his thieving ancestors, which were central to his identity as a master thief. Sly's desire to retrieve the Thievius Raccoonus was not only fueled by his desire to restore his family's legacy, but also to protect it from falling into the wrong hands, specifically those of the villainous antagonist, Clockwerk.