M'kar

M'kar also called the Reborn or the Thrice Born, was a Daemon Prince that was previously a Chaos Space Marine.

Maloq Kartho
His real name was Maloq Kartho and during the Great Crusade he was an Astartes of the Word Bearers Legion. Following Lorgar and the majority of the Word Bearers, he pledged himself to the Ruinous Powers of Chaos Undivided, becoming a Dark Apostle of the Traitor Legion. During the Horus Heresy he tried to destroy the Ultramarines and take over Ultramar. Although he failed and was slain by Ultramarine hero Captain Ventanus, he was eventually rewarded by his Chaos Masters for all the havoc and slaughter he caused, mutating into a Daemon Prince. His hatred for the Imperium of Man and especially of the Ultramarines was enormous and all-consuming.

The Reborn
He eventually manifested in the materium and in M41 (as the Reborn) lead a Chaos invasion fleet in attacking Ultramar again. This time, his fleet was destroyed by a force led by Ultramarines 2nd Company Captain Sicarius. He was next involved in action against the Blood Angels, and specifically their Chief Librarian Mephiston, who he unsuccesfully tried to turn traitor. Some time after his defeat in Mephiston's hands, he reemerged from the Warp and leading a Chaos force took over the Ultramar star fort Indomitable, which was then boarded by Ultramarines lead by Chapter Master Marneus Calgar. Calgar defeated M'kar in single combat, but M'kar's hatred of the Imperium and Ultramar was so strong that it was not possible to banish him to the Warp, even with the help of the Inquisition. The best the Imperials could do was bind M'kar to the warp core of the star fort; this ingenious bond meant that every time M'kar struggled to escape, he would be pulled tighter within the core. The star fort, garrisoned with fully half the 5th Company of the Ultramarines, was then ordered to plot a secret course in the remote, uncharted areas of Ultramar. The fate of M'kar was kept secret: possibly fearing that somebody may try to free him, the "official" Ultramarine version was that Chapter Master Calgar tore M'kar "limb from limb", sending him back to the Warp.

The Thrice Born
About 60 years later, Chief Librarian Tigurius of the Ultramarines had foreseen in a vision the re-appearance of M'kar as a destroyer of Ultramar, although he did not know who the vision refered to apart from being somebody called the Thrice Born. The truth was revealed when Iron Warriors Warsmith Honsou found out the secret of M'kar's imprisonment, and after finding and conquering the Indomitable, set him free as an ally in a new campaign against Ultramar. Donning a desecrated Dreadnought suit the newly rematerialized M'kar bound the Indomitable to a Warp Gate and called forth a huge army of daemons, who along with others under his command in attacking Ultramar, he named the "Bloodborn". He eventually faced Calgar on Talassar, but his essence was completely annihilated after Calgar struck him with the "Shard of Erebus", the same blade that Captain Ventanus had used to slay M'kar's human form during the Horus Heresy.