Marik Ishtar is the leader of the Rare Hunters and the main antagonist of the Battle City arc along with his alter ego. As a child, he was forced to be a tombkeeper by his strict father to continue their family's lineage. This ultimately results in developing a split personality, which is only suppressed by his adoptive brother. Without him, the personality of Yami Marik takes over his body. Marik is often considered to be one of the foremost adversaries in the series. After destroying his evil side and coming to his senses, he returns to Egypt to continue his role as a tomb keeper and becomes an ally of the Pharaoh.
Marik's usual outfit consists of a long purple cape with a gold chain at the front worn by the rare hunters, a sleeveless black shirt and beige combats. He wears gold earrings, neckwear, armbands, and bracelets all up his wrists. His white-blonde hair is neatly arranged as Marik. As a civilian, he still wears the gold earrings, neckwear, armbands, and bracelets all up to his wrists (although in the manga he doesn't wear any of them), a sleeveless purple shirt, blackpants, and black shoes. In the Battle City arc he often wears a KaibaCorp Duel Disk on his left arm.
As a child, Marik was an innocent boy who desired to see the outside world, despite his clan's laws forbidding him from doing so and was willing to sneak out to fulfill his desire. He cared for his siblings very much. Marik also considered Odion to be his brother, despite not being blood related.
Marik bore a grudge towards the pharaoh because he was forced to guard the family carving with his life, robbing him of his freedom. Marik's hatred only intensified when his father forced him to undertake the family's ritual of having the carvings cut onto his back (in the English version the carvings were a tattoo). The pain was so intense that he spawned a second personality to deal with the pain. A year later, when his father brutally tortured Odion for helping Marik and Ishizu to sneak outside, Yami Marik killed his father while Marik was unconscious. Marik woke up with no recollection of his father's murder-only to see Shadi, a loyalist to the Pharaoh and the guardian of the Millennium Items, who had come to warn him about the dangerous path he had taken. Marik thought that Shadi murdered his father, leading to Marik's betrayal of the clan to get revenge against the Pharaoh.
While leading the Rare Hunters in his quest for world domination and freedom, Marik became cruel and uncaring, willing to brainwash people to do his bidding, force them to cheat, and use cruelty on his behalf-the victims included Keith Howard and Strings. He was not above using death to punish his subordinates for failure, such as Arkana and Lumis, nor did he care about sacrificing Rare Hunters to test the fake "The Winged Dragon of Ra" cards which produced severe injuries and death. He even threatened his sister Ishizu with the Millennium Rod for getting in his way and ordered Odion to use the fake Ra card against his will. He still retained his love for his family, despite his mistreatment of them.
Marik's family guarded the tomb of the pharaoh for generations and two of the Millennium Items (the Millennium Rod and Millennium Necklace) were passed on to Marik and his sister Ishizu Ishtar. Marik was forbidden to leave the Pharaoh's tomb due to his father's fear that the freedom and marvels of the outside world would further divert Marik's attention from his heritage. Marik no longer wanted to become a Tombkeeper, so his adoptive brother Odion Ishtar asked if he could take Marik's place but was refused. When Marik was forced to take the initiation ritual to become a full Tombkeeper, Marik spawned a second personality from the pain he endured. A year later, after Marik and Ishizu took a forbidden trip to surface, Marik's father, having found out, attempted to kill Odion. Marik blanked and Yami Marik (the second personality of Marik) emerged for the first time to resist his father's punishment and claimed the Millennium Rod for himself. Ignoring his father's orders to put the item down, Yami Marik used its powers to smash him against the wall. When Ishizu protested, she suffered the same strike. Yami Marik then proceeded to kill his father (or, in the English anime, send his father to the Shadow Realm). Yami Marik was sealed away in Marik's body by Odion.
In the Battle City arc, Marik was the leader of the Rare Hunters organization, as he wished to obtain the three Egyptian God Cards, and with them, unlock their power for himself so that he could gain the title of "Pharaoh" and set his family free. He also had a hidden agenda - to get revenge on the Nameless Pharaoh's soul, which currently resided in Yugi Muto's body, for killing his father, for he mistakenly believed that it was the Pharaoh's fault. In the English anime, he is more fiendish. He wanted the God Cards and the Millennium Puzzle to gain the power of the Pharaoh and rule the world, but he retains his hate of the Pharaoh. Marik uncovered two of the three Egyptian Gods ("The Winged Dragon of Ra" and "Slifer the Sky Dragon") from where Maximillion Pegasus had hidden them away due to the danger associated with them. However, the third Egyptian God, "Obelisk the Tormentor", was taken by Ishizu, who gave it to Seto Kaiba.
Marik and his Rare Hunters hacked into to the Battle City computer system and entered themselves in the tournament. He had them duel Yami Yugi to take the Millennium Puzzle from him and duel Kaiba to take "Obelisk" from him. Marik also had one of his Rare Hunters that he controlled via the Millennium Rod include "Slifer" in his deck and use it against Yami Yugi, but was defeated, allowing Yugi to take Slifer. Later, Marik teamed up with Yami Bakura in a verbal deal consisting of Marik's relinquishment of the Millennium Rod if Yami Bakura could get Slifer back.
Marik, Bakura, and Odion took places in the quarter-finals. Marik took the guise of Namu while Odion pretended to be "Marik" (as nobody except for Yami Bakura had actually met him in person). After Bakura was defeated by Yugi in the first quarter-final match, Marik had Odion use a counterfeit "Ra" card in his quarter-final against Joey Wheeler. When Joey suspected that he was not dueling the real Marik (stating that while Marik was cruel and sadistic, Odion had been dueling with honor as a "True Duelist") Odion was ordered to use the counterfeit to prove his identity as Marik. He was initially reluctant to do this, knowing that he was not worthy to summon the god; however, Marik convinces him to play the card, insisting that by doing so he would prove himself a true tombkeeper. As Odion feared, Ra was angered by this and wrathfully struck both duelists with lightning, ultimately rendering Odion unconscious. In Odion's last moment of consciousness, he reveals to Joey that he is not Marik; at this same time, the real Marik began to suffer sudden headaches. Marik then revealed himself Yugi, Joey, Kaiba, Mai Valentine, Téa Gardner, Tristan Taylor, Duke Devlin, Mokuba Kaiba, and Serenity Wheeler. Suddenly, Marik cried out in pain as his darker personality Yami Marik appeared, having gained control of his body, and announced himself to be the true Marik.
After the quarter-finals, Marik's reformed soul teams up with Yami Bakura to stop Yami Marik, but failed when Yami Marik uses "Ra's" other abilities, which were unknown to Marik. However, Marik (through Téa) warned Ishizu to hide Odion from Yami Marik in order to save his life. In the final duel between Yami Marik and Yami Yugi, their weaker selves were the victims of the Shadow Game being played. As the duel went on, Yami Marik became the dominant host of Marik's body while the real Marik's soul slowly faded out of existence. This Shadow Game gave him a clear edge, for when Yami Yugi lost Life Points, Yugi's body would fade away, when Yami Marik lost life points, the original Marik would fade away. While they dueled, Odion woke up and made Marik realize he had to accept his responsibility for being a Tombkeeper. With this confidence, Marik overpowered his evil self and forfeited, destroying Yami Marik. Marik gave Yugi the Millennium Rod and the Ra card. Marik then revealed the Tombkeeper's initiation. The carving of the pharaoh's memory onto the back of a tomb guardian involves using either a hot dagger (in the manga and the Japanese version of the second series anime), or a tattoo (in the English second series anime, although the dagger was still seen in the flashback) on his back. Fulfilling his duty as a Tombkeeper, Marik returned to Egypt to start a new life.
In the Millennium World arc, Marik, Ishizu, and Odion lead Yugi and his friends to the tomb of the Pharaoh in order for Yugi and Atem to have a final duel in order to determine whether Atem will move on to the afterlife or remain in the present.