Mahaur, also called Mahaur the Harvester, was a Chaos Lord dedicated to the service of Khorne who led the Slaughterkin warband of Chaos Space Marines under the title of Warlord. Mahaur was slain by the intervention of the 5th Battle Company of the Star Phantoms Chapter on the Agri-world of Kerrack during the campaign known as the Scourging of Kerrack in 932.M41.
Before Mahaur fell to the service of the Blood God, he was the Captain of the 3rd Company of the Shadow Hawks Chapter of Space Marines. In 304.M39, after a twelve-standard-year campaign to eradicate rebellious factions within the population of the Hive World Cruach Mhorn, the 3rd Company of the Shadow Hawks were censured for the widespread culling of the population that marked the end of the campaign and left the world unable to fulfil the production quota owed to the Administratum. Rather than accept the dishonour of exile on a penitent Crusade, Captain Mahaur led the survivors of the 3rd Company in a series of raids on Imperial fleets and outposts in the Cruach System before vanishing into the lightless void of the Halo Stars. There Mahaur's fall was complete, as he became a Chaos Lord dedicated to Khorne and became the leader of the Slaughterkin warband.
Mahaur next came to Imperial notice in 913.M41 when an Adeptus Administratum tithe-fleet arrived at the three worlds of the Hreidmal Cluster, seeking the tally of lives and produce due the Emperor as part of the Imperial Tithe, only to find each world laid waste. The headless corpses of each of the worlds' inhabitants lay abandoned, not slain in battle but carefully harvested and their skulls piled in great, towering obelisks. Attempts to demolish these foul monuments brought their creators, the Slaughterkin warband, down upon the Imperial forces, led by Mahaur, and soon the skulls of the Administratum factors and the Astra Militarum regiments assigned to their protection were offered in sacrifice to Khorne atop the rebuilt obelisks.
After the devastation of the Hreidmal Cluster, the Harvester sought to assault the Agri-world of Kerrack in the Varsavus Sector of the Ultima Segmentum in 932.M41. He laid the seeds of rebellion by establishing a series of Chaos Cults, the so-called "Charnel Cults," from among the world's population of primitive agricultural workers who spent their lives harvesting the roots of the world's nutrient-rich Cholam trees for processing into sustenance to support the Astra Militarum regiments engaged in the Karthago Crusade. The cult spread rapidly through Kerrack's population and unleashed a massive rebellion against Imperial rule, and the world soon fell to anarchy and war. The ensuing conflict with the local Planetary Defence Forces and Astra Militarum regiments was fought beneath the dense canopy of the swamp-like Cholam forests and in the air between Imperial Navy pilots and the Hell Talons and Hell Blades brought to the world by the Slaughterkin's arrival after the rebellion had severely weakened the Imperial defenders. The Imperial cause was further damaged when the corruption of Chaos took many of the PDF troops, as they turned to the worship of the Ruinous Powers. Once the Harvester took the planetary capital of Calder's Ark, the victory of the Forces of Chaos seemed assured. Deliverance only came when the 5th Battle Company of the Star Phantoms Chapter of the Adeptus Astartes under the command of Captain Calphax arrived in-system to resupply, and launched an immediate and devastating attack upon the rebel stronghold at Calder's Ark, slaying the Harvester and driving the remaining Traitor Marines of the Slaughterkin from Kerrack.
- Imperial Armour Aeronautica, pp. 76-84
- Imperial Armour Volume Thirteen - War Machines of the Lost and the Damned, pp. 23-25, 33