The Shadow Riders, known in Japan as the Seven Stars Assassins, serve as the main antagonists of the first season of Yu-Gi-Oh! GX, intent on resurrecting the Sacred Beasts. They are composed of 7 Duelists and their leader of varying origins and backgrounds who each have their own agendas. Enlisted by the elderly Kagemaru in his quest to retrieve his lost youth, the Shadow Riders are a group of elite duelists who work towards the goal of reviving the Sacred Beast Cards, Three Phantom Demons). Each of the members that Jaden and company face possess a Shadow Charm, Dark Item in the Japanese Version), similar to the Millennium Items in terms of supernatural power, but of unknown origin. These relics bestow upon their owners different abilities depending on the Shadow Rider in question.
In the past, Kagemaru was forced to seal the Sacred Beast Cards away behind the Spirit Gates underneath Duel Academy due to their inability to grant his wish at that time. In order to access their true abilities, he bestows upon Chancellor Sheppard the seven keys capable of unlocking the Spirit Gates and then pits his subordinates against the school's finest to create the strong dueling presence needed to resurrect the Sacred Beasts cards.
The groups original name, The "Seven Stars" may be a reference to the Biblical Seven Stars in the Book of Revelation. In their debut, only six members were seen; including a silhouette of a member that did not resemble either Abidos or Don Zaloog. It's currently unknown if a different character was intended to be used and scrapped, or simply redesigned. Interestingly said character resembles Sky Scout.