Coyote Diamond
Coyote Diamond - The world's largest diamond, which Fox sent Jackal and Hyena to steal.
History
Xanatos bought it before they could steal it, however, prompting them to attempt to steal it from him, and leading to their attempted assassination of him at Xanadu. (In fact, Fox really sent Jackal and Hyena after the Coyote Diamond as part of Xanatos's scheme to recruit Derek Maza to his cause). ("Her Brother's Keeper")