Rishid is the adopted brother of Marik Ishtar and Ishizu Ishtar. Abandoned in the desert as a child, Rishid is found by the current tombkeeper's wife and taken in. Rishid's mother loved him as her own, but his adoptive father only saw him as a servant. When Rishid found out that they needed a son to carry on their legacy, Rishid asked if he could be that son, which his mother also suggested after their first child was a girl (Ishizu) since a boy had to be the heir of the tombkeeper's, but his father refused. When Marik was born, their father declared him his heir. His mother died during birth, and Rishid held her hand as she died, her last request that he take care of his brother and sister.
Marik and Rishid were close siblings. When Marik was bitten by a cobra and took ill, their father beat Rishid, furious he allowed Marik to be harmed, and ordered he not leave Marik's bedside until he recovered. Marik sees Odion as his brother, despite the fact they are not blood related, and this took away his resentment to Marik, but not his desire to be a tombkeeper.
When Marik's father plans to have the tombkeeper's initiation forced upon his son, Marik admits to Rishid he is terrified. Rishid 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 Rishid to never ask again. When Marik is taken to have the ritual performed, Marik is seen asking Rishid for help, but he stands silently, knowing he cannot interfere. Rishid, fearing what might happen to him as a result, performs his own ritual, carving hieroglyphics on his face with a knife as proof of his loyalty to Marik. 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, Rishid remains behind to keep their father from discovering this. When he does so, Rishid is savagely beaten, a sight that Marik and Ishizu return home to. Their father whips Rishid, and when Rishid falls unconscious, Dark Marik is released. Dark Marik seizes the Millennium Rod from his father and kills him. Rishid wakes up as Shadi appears to warn of the return of the Pharaoh as Marik regains his sense. Rishid, refusing to let Marik discover the truth of his father's death, tells Marik that Shadi killed him.
As a Rare Hunter
Rishid remains by Marik's side for years afterwards, even when Marik betrays the tombkeeper's, presumably because abandoning him would cause Dark Marik to emerge again. He becomes the second-in-command of the Ghouls with Marik. When Marik arrives at Battle City, he has Rishid 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 Rishid pretend to be Marik, drawing suspicion away from the true Marik (neither Yugi or Kaiba had ever seen Marik in person, having only communicated with them via his Millennium Rod through his Rare Hunters. However, Yugi's friends Anzu, Jonouchi, and Ryo Bakura unknowingly had, when they met Marik "helping" Bakura, but he used the name Namu in order to gain both their and the rest of their friends' trust). To help the deception, Rishid 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 Rishid is not aware Marik has placed the card in his deck).
Odion appears during Dark Yugi's duel with Dark Bakura, and pretends to use the fake Millennium Rod to make the spirit abandon his host. This is meant as a ruse to have Dark Yugi forfeit the duel rather than harm his friend. It fails when Dark Bakura repossesses his host and betrays Marik, since for the time being he could not risk Bakura being injured. Rishid then duels Katsuya Jonouchi. During the duel, Jonouchi's friendship with Yugi and his love for his sister Shizuka 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 Sun Dragon Ra", and is horrified to see it as he knows its dangers and that he is not worthy to use it. Jonouchi begins to suspect that Rishid is not Marik: Marik was cruel, cheated, and was a general low-life to Jonouchi, but Rishid has been dueling with honor as a True Duelist. Rishid was about to win the duel against Jonouchi; however, Marik, afraid his deception may be unmasked, commands Rishid to summon the God card to dispel any disbelief. Rishid 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, Rishid 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 Rishid and Jonouchi with lightning. Heartbroken, Rishid did not bother to evade Ra's strikes, and was struck down. Before losing conscious, he saw, to his horror, Dark Marik's awakening, and confessed to Jonouchi that he is not the real Marik and he had a good duel with him. Now comatose, Rishid is taken to his room to rest as Dark Marik emerges.
During the rest of the Battle City arc, Dark Marik returns to Rishid's side again and again to kill him, but is unable to complete the task for a multitude of reasons. When Dark Marik faces Yugi in the final duel, Rishid is awakened from his sleep by the fading spirit of the true Marik, who thanks Rishid for remaining by his side for so many years and being a faithful brother. Rishid stumbles to the top of the Duel Tower, calling for Marik to fight his dark side. With Rishid's encouragement, along with Yugi's "Dimension Magic" card, Dark Marik is destroyed and Marik regains control of his body.
Rishid returns to Egypt with his siblings and is seen in the Memory World arc to see Atem pass on to the afterlife.