Ferrus Manus, (literally "Hand of Iron") the Gorgon, was one of the twenty Primarchs created by the Emperor before the Great Crusade. He led the Iron Hands Space Marine Legion. During his time on the world of Medusa Manus' hands became encased in a hard metallic substance, and he became known for his iron-resolve and disdain for weakness.
Arrival on Medusa
Ferrus was stolen away by the forces of Chaos, just as his brothers were, and spent his first years on the planet Medusa. As a youth, he discovered an "X" mark on the pod that first brought him to this world and that the chamber was too precise to be a natural formation. Exploring further, he discovered runes and electro-conductive stalagmites all around the chamber. His inspections awakened an imprisoned colossal bio-mechanical worm-like creature, which attacked him and escaped, ignoring his attacks. He followed its path of destruction and swore he would destroy the beast he had unwittingly released. When he reached the surface, he saw other men in the distance but wouldn't reveal himself to them, instead keeping his recent oath in mind.
Years later, Ferrus walked unscathed and fully formed from the mountains where he encountered the roaming clans and tribes of Medusa. Ferrus would not join these tribes, as many of his brothers did. Instead, he sought out physical challenges to make himself stronger and more resilient. These tests ended with his battle against the Great Silver Wyrm Asirnoth, a metallic beast impervious to harm; Ferrus had to drown it in magma to kill it. The melted flesh of the wyrm fused to Ferrus's flesh, giving him the true metal hands his Legion would take its name from. Ferrus returned to the tribes and lectured them on technology. The clans advanced at a stunning pace and Medusa prospered, but Ferrus took care to leave the inter-clan rivalry and fighting by never taking sides, as he saw the competition between them as healthy and good.
The Emperor eventually came to Medusa and Ferrus Manus tested himself on him in a cataclysmic battle that is said to have lain waste to entire mountains. Finally having found someone equal, Ferrus accepted the Emperor as his master and took command of a legion of Space Marines.
Thousands of planets would fall to the remorseless Iron Hands under Ferrus's leadership. Each weak link in humanity was to be purged if mankind was to grow stronger. Scholars spoke of the wave of piety and faith that spread before the Iron Hands, with many planets suddenly motivated to look into themselves when they heard that the Iron Hands were approaching[Needs Citation]. During the Great Crusade the Iron Hands battled the Human Diasporex alongside the Emperor's Children. This was symbolic of the bond shared by Ferrus Manus and the Emperor's Children Primarch Fulgrim, who were close friends. However during the Conquest of One-Five-Four Four he received visions from the Eldar alluding to his eventual demise at Fulgrim's hands. Distrustful of the Xenos, Ferrus rejected the prophecy.
Ferrus was one of the four primarchs privately referred to by Roboute Guilliman as "the Dauntless Few", the four of his brothers who most exemplified their father's design and whose Legions reflected their best qualities (the others being Rogal Dorn, Sanguinius, and Leman Russ)
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 were 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.
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.
The Draor Obelisk
'On the eighteenth day of Nureg, the Guardian of Terra did alight on Draor and there was a great star-fire in the heavens as seven ships of gold descended. And, lo, did the men of Iron kneel to his will and the will of the Avenging Son. He brought his word and his bond, but it was the gift of bone the men of Iron took heed of. And so reunited with their patriarch was a pact with the men of Iron sealed and the Imperium of Man reunited. Never again would it be put asunder.’ 
On the world of Draor, Inquisitor Kinebad, accompanied by a companion named only as 'Scar-borne', uncovered an ancient Obelisk detailing a pact made between Guilliman, Dorn and the Shattered Iron Hands legion. In return for their adherence to the nascent Codex Astartes, the Iron Hands were returned the Skull of Ferrus Manus. How exactly Guilliman and Dorn retrieved the skull is unknown.
Following the Drop Site Massacre, a mentally volatile Fulgrim would have Fabius Bile clone Ferrus. However these clones proved unstable and each refused to turn against the Emperor, forcing Fulgrim to once again kill his brother and driving him even madder.[Needs Citation]
Ferrus Manus' primary weapon was the gigantic Thunder Hammer Forgebreaker, crafted for him by Fulgrim. Manus wore a finely-wrought suit of Cataphractii Pattern Terminator Armour known as the Medusan Carapace. More than a simple suit of armor, it possessed many servo mechanisms and support systems. He was also seen fighting with a wrench-shaped Power Weapon.
Ferrus Manus is Latin for "Iron Hand."
|I - Lion El'Jonson · II - Unknown · III - Fulgrim · IV - Perturabo · V - Jaghatai Khan · VI - Leman Russ · VII - Rogal Dorn · VIII - Konrad Curze · IX - Sanguinius · X - Ferrus Manus · XI - Unknown · XII - Angron · XIII - Roboute Guilliman · XIV - Mortarion · XV - Magnus · XVI - Horus · XVII - Lorgar · XVIII - Vulkan · XIX - Corvus Corax · XX - Alpharius Omegon|
- 1: Iron Hands (Novel) by Jonathan Green[Needs Citation]
- 2: Fulgrim (Novel) by Graham McNeill[Needs Citation]
- 3: The First Heretic (Novel) by Aaron Dembski-Bowden[Needs Citation]
- 4: Angel Exterminatus (Novel) by Graham McNeill Book 2 As Above so Below - Theogonies II
- 5: Know No Fear (Novel) by Dan Abnett, Ushkul//Thu, Chapter Two, pg. 350
- 6: Wrath of Iron (Novel) by Chris Wraight, Chapter Fourteen, pgs. 249-250
- 7: Rebirth (Novel) by Nick Kyme: Epilogue, pg. 378
- 8: Imperfect (Short Story) - Death and Defiance (Anthology)
- 9: Warmaster (Audio Book)
- 10: The Horus Heresy - Book Two: Massacre pgs. 234-235
- 11: Feat of Iron (Novella)[Needs Citation]
- 12: Index Astartes: The Iron Hands