Effectively the Legion's Chief Librarian, Targutai had fought alongside Jaghatai Khan since their youth on Chogoris. Yesugei was known for his very close relationship to the Khan, serving as his chief adviser and de facto number two within the Legion. During the Council of Nikea, Targutai argued in favor of the responsible and limited use of Librarians and Psykers in Imperial use and said they would be a powerful weapon against the enemies of mankind. During the Heresy Yesugei was based on Chogoris while the Great Khan was waging the Chondax Campaign, but sensing something was amiss rushed to meet up with him.
In the Warp Yesugei's ship encountered a Sons of Horus vessel which turned out to have been captured from survivors of the Drop Site Massacre. Learning of the Horus Heresy from the Salamanders Captain Xa'ven, Yesugei and his new teammates journeyed to warn Jaghatai Khan of Horus' treachery, battling Word Bearers along the way. Plagued by dreams of Jaghatai's death, Yesugei and his new comrades eventually makes their way to Prospero using his own Frigate Sickle's Moon along with captured traitor vessels. Yesugei directed his small fleet against the Death Guard flagship Endurance, saved from destruction only thanks to Jaghatai Khan, who managed to take command of his fleet after foiling a coup by pro-Horus conspirators led by Hasik Noyan-Khan.
Four years later, Yesugei was one of the few White Scars who had not lost faith in victory or had become demoralized during the grueling attritional war against the traitors, and believed that a path back to Terra would be found. That path eventually materialized in the form of the Dark Glass station, which Yesugei boarded in an attempt to study. However as the Battle of Catallus raged, Veil, an agent of the Navis Nobilite who had infiltrated the White Scars fleet, managed to cause the station's destruction with vortex charges. As the station died, Yesugei attached himself to its command throne and painfully sacrificed himself to force open a portal into the Webway. As his body disintegrated, Yesugei sent his psychic goodbyes to his three closest companions: Jaghatai Khan, Ilya Ravallion, and Revuel Arvida. The portal allowed the Scars to return to Terra, where they proved instrumental in defending against Horus' siege.
Yesugei was the father of Genghis Khan, whom Jaghatai Khan is based on.