Marr Idi-Shael, a Cerean with exceptional mathematical abilities and sensitivity to the Force, was a male who served as the first mate aboard the starship Junker. He spent numerous years conducting salvage operations alongside his companion, the Captain Khedryn Faal.
Following an encounter with Jedi Knight Jaden Korr and a brief period of informal Force instruction under Master Relin Druur in 41 ABY, he requested admittance into the New Jedi Order, subsequently becoming Jaden Korr's apprentice.
Marr and Khedryn Faal had been partners for a considerable time by 41.5 ABY. Their adventures led them to places like Fhost, where they frequented the Black Hole cantina for games of sabacc. During one such game, the local crime lord Reegas Vance attempted to seize the coordinates of a Frozen moon discovered by Khedryn and Marr, intending to claim them as his prize. However, Jaden Korr, utilizing the Force to manipulate the card shuffler in Khedryn's favor, thwarted this attempt. Accusations of cheating led Reegas to order his Weequay bodyguards to attack. The ensuing conflict resulted in the death of Earsh. Ultimately, Jaden, Marr, and Khedryn managed to escape through a back exit.
Marr played a crucial role in assisting Jedi Master Relin Druur in boarding the Harbinger. He initiated a micro jump, positioning the Junker directly in front of the Harbinger's shields, and then breached them using a Powercrystal.
While he was aiding Relin in boarding the vessel, the Junker was infiltrated by five Massassi warriors. Unable to combat them directly, Marr utilized his newly discovered Force abilities to pilot the Junker blindly out of the landing bay. Subsequently, he exposed the ship to the vacuum of space, eliminating the Massassi, but not before sustaining severe injuries himself. With his remaining strength, he set the Junker on autopilot, directing it toward a frozen moon where he knew he could find Jaden Korr and Khedryn Faal, as the Harbinger met its end in the moon's atmosphere.
After Korr and Faal tended to his wounds, Marr conveyed Relin's final words to Korr. He then expressed his desire to receive Force training and become a Jedi, a request to which Jaden agreed.
During their journey back to the frozen moon, Jaden commenced Marr's Force training, which involved disassembling and reassembling Jaden's old lightsaber and guiding him through lightsaber exercises. Upon the Junker's arrival at Fhost, they discovered that a medical facility was under attack by clones. Jaden and Marr infiltrated the facility and split up to locate the clones. By the time Marr rejoined Jaden, Jaden had already been subdued by the surviving clones, who then escaped aboard a stolen medical supply ship, taking Khedryn with them.
Marr and Jaden tracked the supply ship to a remote system in the Outer Rim. Upon their arrival, they were contacted by Nyss Nenn, who was also on the supply ship. Nyss offered to exchange Jaden, equipped in a hardsuit, for Khedryn, who would be released in an escape pod. Jaden accepted the offer, but during the transfer, his hardsuit was compromised, necessitating Marr to don a hardsuit and rescue him as well.
The reunited crew then pursued the supply ship once more, eventually discovering an ancient Rakatan space station. Jaden and Marr boarded the station and engaged in combat with numerous beings controlled by the station, ultimately defeating them. As they ventured deeper into the station, they were attacked by Nyss, and Marr was knocked unconscious. Upon regaining consciousness, he found that Jaden had killed Nyss, but he also encountered a clone of Jaden, the Iteration, standing over him. The Iteration fatally stabbed Jaden in the temple with a mindspear. Marr confronted the Iteration and, initially outmatched, tapped into the Force and defeated him. Marr then utilized the mindspear and the Iteration to transfer Jaden's identity and consciousness into his cloned body. Shortly thereafter, Soldier, another clone of Jaden, arrived, pursued by Mother in Seer's body. The three of them held off Mother while Khedryn rigged the supply ship to self-destruct. Jaden, Khedryn, and Marr escaped in the Junker as the station exploded.
His innate connection to the Force enabled him to calculate hyperspace jumps without the need for a navicomputer. Furthermore, Idi-Shael demonstrated the rare ability to absorbing energy, evidenced by his capacity to halt the lightsaber blade of Iteration with his bare hands during their duel.