Odion, known as Rishid in the manga and Japanese anime, is the adoptive brother of Marik Ishtar and Ishizu Ishtar. Throughout the series he remains loyal to Marik, even when mistreated. In the Singaporean English anime, he has been called by three names, Rishid, Rishido and Odion.
Odion is the adopted brother of Marik Ishtar and Ishizu Ishtar. Abandoned in the desert as a child, Odion is found by the current tombkeeper's wife and taken in. Odion's mother loved him as her own, but his stepfather only saw him as a servant. When Odion found out that they needed a son to carry on their legacy, Odion asked if he could be that son, which his mother also suggested, but his father refused. When Marik was born, their father declared him his heir. His mother died during birth (this isn't stated in the dub, but is implied), and Odion held her hand as she died, her last request that he take care of his brother.
Marik and Odion were close siblings, but Odion always harbored a resentment for him as the true heir to the tombkeeper's and legitimate son of his parents. When Marik was bitten by a cobra and took ill, their father beat Odion, furious he allowed Marik to be harmed, and ordered he not leave Marik's bedside until he recovered. Odion takes a dagger to Marik's room with the intent to kill him in his sleep (this is edited out in the dub, along with Rishid's resentment for Marik). Marik awakens and murmurs "brother", causing Odion to drop the weapon in shock: Marik sees Odion as his brother, despite the fact they are not blood related.
When Marik's father plans to have the tombkeeper's initiation forced upon his son, Marik admits to Odion he is terrified. Odion asks his father once again that he be chosen instead, as Marik is young and scared. His father once again denies his request and refuses, ordering Odion to never ask again. When Marik is taken to have the ritual performed, Odion, fearing what might happen to him as a result, performs his own ritual, tattooing hieroglyphics on his face as proof of his loyalty to Marik. (In the Japanese anime, he carves the hieroglyphics on his face with a knife.) This mark later becomes critical to sealing away the true darkness that becomes seeded in Marik during the ritual: Marik's other personality. When Marik and Ishizu sneak away on a trip to the surface, Odion remains behind to keep their father from discovering this. When he does so, Odion is savagely beaten, a sight that Marik and Ishizu return home to. Their father whips Odion, when Odion falls unconscious (this is edited out in the English anime, so it isn't how Odion fell unconscious), Dark Marik is released. Dark Marik seizes the Millennium Rod from his father and kills him. (In the English anime, he is sent to the Shadow Realm.) Odion wakes up as Shadi appears to warn of the return of the Pharaoh as Marik regains his sense. Odion, refusing to let Marik discover the truth of his father's death, tells Marik that Shadi killed him.
Odion remains by Marik's side for years afterwards, even when Marik betrays the tombkeeper's, presumably because abandoning him would cause Yami Marik to emerge again. He becomes the second-in-command of the Rare Hunters (Ghouls in the Original) with Marik. When Marik arrives at Battle City, he has Odion duel and collect 12 Locator Cards, enough for both of them to enter the finals. (They each needed 6 to participate) Marik enters under the guise of Namu while he has Odion pretend to be Marik , drawing suspicion away from the true Marik (neither Yugi, any of his friends, or Kaiba had ever seen the real Marik). To help the deception, Odion is armed with a fake version of the Millennium Rod and a copy of Marik's Egyptian God card, The Winged Dragon of Ra (although Odion is not aware Marik has placed the card in his deck).
Odion appears during Yami Yugi's duel with Yami Bakura, and pretends to use the fake Millennium Rod to make the spirit abandon his host. This is meant as a ruse to have Yami Yugi forfeit the duel rather than harm his friend. It fails when Yami Bakura repossesses his host and betrays Marik, since for the time being he could not risk Bakura being injured. Odion then duels Joey Wheeler. During the duel, Joey's friendship with Yugi and his love for his sister Serenity reminds him of his mother and the relationship he once had with Marik, while his brother continues to order him through the Millennium Rod.
Odion draws "The Winged Dragon of Ra", and is horrified to see it as he knows its dangers and that he is not worthy to use it. Joey begins to suspect that Odion is not Marik: Marik was cruel, cheated, and was a general low-life to Joey, but Odion has been dueling with honor as a True Duelist. Marik, afraid his deception may be unmasked, commands Rishid to summon the God card to dispel any disbelief. Odion does not want to risk the task, but Marik convinces him that if he can do so and control Ra, he will have proven himself a true tombkeeper. Excited by the thought of being accepted into the clan, as he always wished, Odion summons the God Card, but factors, such as his lack of a real Millennium Item and the card being a fake, incurs the god's wrath, striking Odion and Joey with lightning. Heartbroken, Odion did not bother to evade Ra's strikes, and was struck down. Before losing conscious, he saw, to his horror, Yami Marik's awakening, and confessed to Joey that he is not the real Marik. Now comatose, Odion is taken to his room to rest as Yami Marik emerges.
During the rest of the Battle City arc, Yami Marik returns to Odion's side again and again to kill him (in the Dub Send him to the Shadow Realm), but is unable to complete the task for a multitude of reasons. When Yami Marik faces Yugi in the final duel, Odion is awakened from his sleep by the fading spirit of the true Marik, who thanks Odion for remaining by his side for so many years and being a faithful brother. Odion stumbles to the top of the Duel Tower, calling for Marik to fight his dark side. With Odion's encouragement, along with Yugi's Ragnarok card, Yami Marik is destroyed and Marik regains control of his body.
Odion returns to Egypt with his siblings and is seen in the Memory World arc to see Atem to the afterlife.
Odion uses a Trap Deck comprised primarily of powerful Trap Cards. His signature card is the Field Spell "Temple of the Kings" which allows him to activate Trap Cards on the same turn they are Set, as well as limiting the amount of Spell and Trap Cards his opponents can play. It also allows him to summon his strongest monster, "Mystical Beast Serket". Odion duels passively due to his reliance on traps, only going on an offensive once his "Trap Monsters", "Embodiment of Apophis", are activated. In the Battle City Finals Odion's deck also contained a counterfeit version of "The Winged Dragon of Ra" placed in his deck by Marik, though Odion was reluctant to use the card. Odion has a considerable number of off-screen victories with the deck, after he had to collect 12 Locator Cards for himself and Marik to enter the Battle City finals.