Julius Kaesoron was the First Captain of the Emperor's Children Legion during the Great Crusade and the Horus Heresy. He was present during many of the most infamous campaigns of the Heresy, including the Istvaan III Atrocity and the Drop Site Massacre of Istvaan V, and was one of the first Noise Marines, or "Kakophoni" as they were originally known, among the Heretic Astartes. Though it appeared that Kaesoron had met his ultimate fate on Istvaan V, it seems that Slaanesh, the Prince of Chaos, was reluctant to let such a promising servant die, and Kaesoron was later resurrected as a Daemon Prince.

He made his presence known in the material universe once again in 812.M41, on the Hive World of Shardenus during the Iron Hands' campaign to retake the rebellious Contqual Sub-sector. The Daemon Prince Kaesoron was confronted by a small group of Iron Hands Librarians and Lord Clan Commmander Arven Rauth himself, before finally being defeated and banished back into the Warp from whence he came.