Maledictum

The Maledictum was a powerful artifact of Chaos that was hidden on planet Tartarus. It held an extremely powerful daemon of Khorne that had been imprisoned within by the Eldar, possibly the Biel-Tan, who are seen protecting it later. The artifact was able to influence the humans on Tartarus, driving them to hide it in order to insure that the Ordo Malleus daemon hunters – who would destroy it – could not find the Maledictum.

Dawn of War

In Warhammer 40,000: Dawn of War, an Ork horde is attacking Tartarus and the Blood Ravens 3rd Company under Gabriel Angelos arrives to help the Planetary Defence Force. They soon discover that Chaos Space Marines of the Alpha Legion, led by Chaos Lord Bale and Sorcerer Sindri Myr, have actually instigated the Ork invasion as a distraction for something more important.

The Blood Ravens run into Biel-Tan Eldar led by Farseer Macha, who are aiming to hide any evidence pointing to the existence or location of the Maledictum. With all the mayhem going on – the Ork invasion, the Space Marines fighting the Eldar, and the Maledictum corrupting local population – the Chaos forces manage to discover the artifact and the means to unlocking it. Isador Akios, a prominent Librarian of the Blood Ravens and a personal friend of Captain Angelos, is corrupted by the Maledictum and attempts to claim it, but Sindri Myr intervenes and takes it for himself.

The enraged Blood Ravens hunt down the traitor forces and Angelos personally executes Akios, while Sindri Myr betrays Bale and escapes with the artifact. He uses its power to transform into a Daemon Prince, forcing an uneasy alliance between the Blood Ravens and the Biel-Tan. They manage to destroy Sindri, and Angelos – despite Macha's frantic warnings – uses the God-Splitter to destroy the Maledictum. This, however, with all the recent deaths on Tartarus functioning as sacrifices to power the imprisoned daemon, merely releases it. After a discussion with Angelos, the daemon departs without violence, although it announces it will return to "claim you all".

Dawn of War II: Retribution

Theory - Recovered from left over audio files within the game, Angelos states that the messenger of Khorne that Kyras speaks of is the daemon from within the Maledictum.

A different audio file states that the being called Kyras is not alone. Which leaves some to believe the daemon of the Maledictum returns for the final battle on Cyrene by merging with the traitor Blood Raven Chapter Master Azariah Kyras.