Enraged, Ferrus Manus attacked Fulgrim, which lead to a short duel and eventually to the death of a Primarch! Who was the first Primarch to die?
Via our good friends at Lexicanum
Once swayed himself to the side of the Warmaster, Fulgrim approached Ferrus Manus before the heresy and tried to lure him to join Chaos. Ferrus Manus was so enraged at this proposal that he attacked Fulgrim. A short duel took place, where Ferrus destroyed Fulgrim’s sword Fireblade, the same weapon Ferrus had given to him many years before. Fulgrim escaped after rendering Ferrus unconscious, leaving him alive but taking with him the massive Thunder Hammer Forgebreaker he himself had crafted for his brother.
The Iron Hands was one of the loyal legions the Emperor called to Isstvan V. Given the large distance, Ferrus Manus took the Legion’s fastest ships and departed only with his veterans. Most of them died in this battle, when following the loss of their primarch they were struck down by the traitor legions, caught between the hammer of the Emperor’s Children and upon the Anvil of the four support legions of the second wave.
Fulgrim personally killed Ferrus during the battle at Isstvan V, using the daemon weapon he acquired fighting the Laer to strike his head from his shoulders in one fell swoop. Fulgrim, distraught with grief that his closest brother was dead by his own hand, was soon thereafter possessed by the daemon within the sword. The possessed Fulgrim then delivered Ferrus’s head to Horus.
When Guilliman heard reports that Ferrus had fallen, along with Vulkan and Corax, he lamented that, of the three, he would miss Ferrus most of all.
Later during the Heresy as Horus fell deeper and deeper into Chaos and his mental state perhaps began to deteriorate, he took the skull of Ferrus Manus, mounted it on his throne, and began to increasingly speak to it. During their one-sided conversations, Horus lamented that he only had bloody-handed tyrants, mass murderers, and daemons for his generals instead of strategists and men of duty like Ferrus.
Ten thousand years later, a daemonette of Slaanesh taunted Iron Hands Sergeant Naim Morvox on Shardenus, claiming that it had seen Manus’s head, and “it is still screaming.”