The Millennium Rod (千年ロッド Sennen Roddo) is a Millennium Item. It is often referred to as the "scepter" in the Japanese version.
Upon Dark Marik's awakening, he took the Millennium Rod and used the blade to kill his own father (skinning his back off in the manga, stabbing him to death in the Japanese anime, and sending him to the Shadow Realm in the English dub). After that, Marik took the Rod to assist him in his quest for world domination. In the English dub, Marik planned to collect all three Egyptian God cards and the Millennium Puzzle to become King. However in original Japanese version, he stated that after he gets his revenge, the Rod would be useless to him, and that he would have no qualms of giving it to Dark Bakura. After Marik's defeat at Battle City, he gave the Millennium Rod to Yugi.
A false Millennium Rod was created and given to Odion Ishtar, who was disguising himself as Marik at the time, in order to play his role more realistically. While Odion wielded the false item, Marik (under the pseudonym "Namu") utilized the real Rod's powers in secret, to make it look like Odion is the wielder of the item. When Odion played a false God Card Ra, it incurred the Gods' wrath and caused a lightning bolt to strike down Odion, shattering the false Millennium Rod, revealing Odion's true identity.
In Seto Kaiba's Duel with Ishizu Ishtar, the Millennium Rod showed Kaiba a vision of his past incarnation and the Blue-Eyes White Dragon, causing him to summon it instead of attacking with Obelisk the Tormentor (which would have caused him to lose the duel). This is because it was originally owned by the Egyptian Priest Seto, of whom Kaiba is a reincarnation. Its use in Egyptian times was to seal the Ka hiding inside of people into stone tablets.
In Yu-Gi-Oh! Forbidden Memories, the Rod is shaped and colored slightly different. It is also owned by Kaiba in the modern day instead of Marik.
Out of all the Millennium Items, this one's has demonstrated the most in terms of raw power. This item's unique ability grants the holder the power to control the minds of others, and also lets its owner telepathically communicate with his servants, as well as look into the network of their memories, akin to the Mind Scan, and cast illusions such as when Marik made Arkana believe his key had disappeared to the point where he cannot see or feel it.
Just like the other Millennium Items, its power over the Shadow Game allows it to materialize and command Duel Monsters and their effects, cast a Penalty Game on the loser of a game, alter minds, and manipulate souls.
Its other abilities allow the owner to use a telekinetic-like attack to force an opponent back, and to paralyze them. A victory duel is not required to use these abilities. In the Virtual World arc, Marik commanded the Rod to unleash destructive lightning to destroy the machinery in Noah's undersea fortress.
There is also a short sword concealed in the bottom of the rod, although this was only used in the Japanese Anime and Manga. The shaft of the rod acts as the sheath. This is removed in some of the dubbed anime. In the original Japanese version, this knife was used for the Ishtar clan for carving the symbols on their first born male heir's back. Marik Ishtar was one of the many to endure this painful ritual, against his will, which gave birth to his dark side, Dark Marik.