The Thevius Racceenus is a book handed down from generation to generation in the Cooper family. The book contains secret sneaky thieving moves that have been created and handed down for hundreds of years within the Cooper Clan. It wasn't just a book, it was a legacy. A legacy that was taken from its owners, but was soon to be taken back by those who deserve to have its secrets.
In the first game, Sly Cooper and the Thevius Raccoonus, Sly is shown as a young little raccoon. The infamous Thevius Raccoonus, the book of his elders, was stolen from his family, who were then slain at the hands of the devilish group of misfits known only as the Fiendish Five. They ravaged Sly's home, destroyed his family, took the Thevius Raccoonus, tore the book into five pieces and left Sly for dead, all alone.
Sly Was put into an orphanage where he met Bentley and Murray his two best friends, and eventually, his partners in crime. After a few jobs here and there, honing their skills for bigger and better things, the gang was then on the first big mission of their lives: To find the members of the Fiendish Five, destroy them, and get back what is rightfully Sly's, the Thevius Raccoonus.