Autek Mor
Autek Mor aka The Maimed or Moonman was the Iron Lord and Iron Father to the infamous Clan Morragul of the Iron Hands legion during the Great Crusade and Horus Heresy, later becoming the first Chapter Master of the Red Talons. One of the original members of the Legion prior to its reunion with Ferrus Manus, he served in the Unification Wars on Terra and the reconquest of the Sol system. When the X Legion was reunited with their primarch, Mor had developed a reputation for being an excellent weaponsmith and a huge asshole. He ruled his clan company with an iron fist, and was known to have killed other members of his legion in duels over slights to his honour. When Ferrus was rediscovered and the Legion claimed Medusa as its new homeworld, Mor took over an outlaw clan's leviathan crawler in a single night of violence and made it his. As the years went by, Clan Morragul became a dumping ground for outcast, insubordinate, and unstable elements of the Iron Hands, who fought and died under Mor's command. He also didn't really get on well with Ferrus, having no love for each other. As such he and his clan had a shitty reputation and were generally regarded as outsiders in the Iron Tenth. Of course, Mor couldn't give a fuck about any of that.
When the biggest family drama began, Clan Morragul was part of the second wave of Iron Hands forces to arrive at Istvaan V. Unfortunately, his arrival was at the same time the Night Lords, Iron Warriors, Word Bearers and Alpha Legion pressed the "change team" button. Though they never really liked each other, Mor valiantly tried to break through the traitor fleet to rescue Ferrus and the rest of the Iron Hands on the ground, unwilling to accept his primarch's demise. Alas, he was forced to retreat and escape with a handful of survivors.
While Shadrak Meduson rallied many of the survivors from Istvaan V and fought guerrilla style, Autek Mor said "fuck that" and went about making war his own way. He gathered what forces would rally to his banner and launched a series of full-scale assaults upon worlds that the Traitor Legions had captured or turned, allowing them to expend their strength and then destroying what remained with overwhelming force. It was a brutal strategy in which entire populations were to be allowed to fall while the Iron Hands stayed their wrath, yet it was one that made full accounting of the relentless calculus of war. With their force blunted by their invasion operations, the traitors could be attacked at the moment of their supposed victory whilst at their weakest and obliterated without mercy.
Mor especially punished worlds that simply surrendered to the traitors without fighting. One such planet was retaken from the traitor forces, only for Mor's troops to immediately take off. Right as the inhabitants were beginning to celebrate their liberation, the timed atomic devices that Mor had set under all their major cities detonated, turning the planet into a radioactive ball of rock. As far as Mor was concerned, anyone who surrendered without a fight was filthy traitor scum and deserved to be treated as such. By destroying such worlds, he was sending a clear and unequivocal message: you were either for the Imperium or against it. There was no middle ground, and if you were against it you could expect the same treatment. What a dick. This, however, would be nothing compared to what he did next...
Marshaling a force of Solar Auxilia, as well as elements of the Imperial Fists, Autek Mor attacked the planet of Bodt, the fief world of the World Eaters where Angron had first taken command of his legion. Now, Mor could've done his usual thing and attacked Bodt with maximum rip and tear, but then he realized that just wasn't metal enough, and so decided to crash the FUCKING MOON INTO THE PLANET instead. The entire population of Bodt--traitor Marines, Sarum Mechanicum and Legio Titanicus--was destroyed, which not only was a blow to the World Eaters' recruitment but to the overall traitor cause. Mor himself didn't participate in the main assault. Instead, he spent the battle retrieving a stasis casket with unknown contents from a hidden vault beneath Bodt's surface while the rest of the planet was mooned into oblivion.
After the Horus Heresy, Clan Morragul became the Red Talons Chapter and Mor became its first Chapter Master.
TLDR: Autek Mor was the angriest toaster marine in a legion of toaster marines and he got shit done.
Former Thunder Warriors
Mor's borderline (being generous with that) insane aggression has lead to even in-universe speculation that he isn't your run of the mill Iron Hand, and that something was different in his creation. His habits and mannerisms also mirror that of behaviors seen in known Thunder Warriors like Ghota and Arik Taranis. Combined with the fact that he was one of the very first legionaries created for the Iron Tenth, and with hints that there may have been other Thunder Warriors hidden among the Astartes, like Endryd Haar (and possibly also Enoch Rathvin, legion master of the Sixth before the discovery of Fur Daddy), some have come to suspect that Autek Mor may have also once been a Thunder Warrior.
It's been hinted, at least in Haar's case, that the Astartes production process was still being retooled from Thunder Warriors to Astartes in Terra's geneworks, with Haar being one of only four in his presumably large induction group to survive the implantation process. This would explain why some of the earliest Astartes had Thunder Warrior-like attributes among Astartes such as being unusually angry, unusually big-ass motherfuckers who solve arguments among their underlings using power fisting unusually often, before the process was turned down a bit. This is somewhat unsteady though given that not all of the first gen Astartes were like that and there are plenty of contradictory hints dropped by GW like such as "do you dream of thunder?" (Haar) or "the origins of his geneseed or perhaps his bloodline were not as they should be" (Mor). It's not like we'll ever know either way.
On the Tabletop
Horus Heresy 1.0
He's an Iron Father with Cataphractii Terminator armor, +1S, +1T (but -1In and -1 attack), a Servo-Arm, a Paragon Blade and a Volkite Charger for gear. With Fearless, the Iron Father upgrade and Preferred Enemy (Infantry) Mor is a complete and utter goddamn beast with 3 base attacks (S6 w/ 6's to-wound causing ID) +1 Servo arm attack (S8 w/ Unwieldy). All of that at AP2. Oh, and with Inviolate Armour and T5 he can't be ID'ed by double Toughness from shooting.
Horus Heresy 2.0
Autek's stats have effectively been reversed this edition. His S and T have both gone down by one, but he gets +1In and +1A and an extra wound to compensate, and his saves remain formidable (2+/4++, 5+ FNP), so he's still a burly motherfucker. He's also gained Relentless and a cyber-familiar in exchange for his cortex controller and Jealous Command. His servo-arm is replaced with a manipulator array that is S6 and has Shred, Armourbane, Precision Strikes (3) and Unwieldy, and his paragon blade has been swapped for a two-handed AP2 axe with Reaping Blow (2). He also has a new warlord trait, Tyrant's Wrath: whenever he joins an Iron Hands unit, that unit may add an extra wound when calculating the results of close combat, but if they do so they also take one wound, no saves allowed. They also get an extra Reaction during the opponent's shooting phase.