Once a proud and arrogant successor chapter of the Ultramarines, the Marines Triumphant were founded during the Twenty First Founding, colloquially known as the Cursed Founding. Despite the unfortunate fates many chapters from that time suffered, the Marines Triumphant continued on in their service for several millennia without issue, purging the enemies of the Imperium. In early M41, after thousands of years of service, the Marines Triumphant were called upon to do battle with the forces of Chaos on the agri-world of Jathea XII. During the battle, the Warband summoned a daemon, who rampaged through the Marine's lines and causing massive damage and casualties. Eventually, the Marines managed to defeat the daemon; however, before it disappeared into the Warp, it placed a curse upon the Marines Triumphant, poisoning their gene seed and preventing them from producing more progenoids and Black Carapaces, leaving them unable to produce more Marines and dooming them to a slow demise.