Abidos the Third is an ancient pharaoh. He has never lost a Duel in his life.
He regained his human body by the powers of his Shadow Charm, the Shadow Headband. He then became one of the Shadow Riders. He and his army of mummies abduct the "Keykeepers" to his flying ship in order to Duel them and take their spirit keys.
While dueling Jaden, he realizes that he had never lost a Duel because he only duelled his underlings. They were simply too scared of him, so they would always let them win, just because he was a pharaoh.
Jaden defeats him quite easily, and Abidos realizes what a real Duel is like. He accepts his loss and gives his Shadow Charm to Jaden. He then leaves for the afterlife. He uses a "Servants of the Pharaoh" Deck, with Monster Cards which greatly resemble his own servants.