When the Horus Heresy began, they believed their revered leader that it was the Emporer who had betryaed them and that only the legions could lead humanity to its ultimate purpose of domination of the galaxy. Throughout the Heresy, they maintained their discipline and focus on tactical objectives, even as others gave in to the temptation to kill and destroy for its own sake. As the discipline of many of the younger companies eroded over the years, their veterans became less orderly and their units became known as Reavers, allowing the destruction of their enemies to become their overriding priority. These Terran veterans continued to conduct war in their Legion's old ways, with precisely timed and coordinated attacks on tactical objectives.
It was not until the final Siege of Terra that they realized that Horus had sided with the dark gods of Chaos over humanity itself. There had been clues of the dark path their leaders strode, but the men's loyalty was absolute and they refused to believe that the men who personally led them to the conquest of the galaxy could be wrong. When the realizaiton finally came, too obvious to deny, their psyches cracked under the strain of reconciling this reality with their all-powerful indoctrination of loyalty to the legion and Horus. The purpose of their existence had been not only destroyed, but twisted into the antithesis of everything they believed in and had spent many lifetimes fighting for. For them, all that was left in the universe was betryal, hatred, dishonor and death. The company gathered together outside the gate of the Imperial palace and made a suicidal attack into the teeth of the defenses. Their minds blackened beyond despair, their only hope for salvation lay in death in battle with a worthy foe.
I wanted them to really stand out from the rest of the army and to look like older, Terran veterans. They have a mix of MkII and MKIII (mostly III), where the rest of the Legion will have MkIV - VI. I also added the Spartan crests to the helmets to have a bit more of the Roman Legion look of the original legions, but it also works with the mohawk motif of the Cthonian ganger influence so it still fits with the Sons of Horus style, in my mind. I tried to convey their elite status with their equipment as well. Obviously they are loaded with power weapons and special weapons and a vexilla. I also made sure to include the extra melee weapons, multiple grenades, pouches and even a pistol holster (some of these details are not too easy to see in the photos due to the angle of the shots and the shadows). I also wanted their poses to stand out, with multiple guys either crouching or running. I wanted to give the idea of a unit where some men are stopping to provide covering fire while others rush forward. And the sergeant has a bionic leg to show he has survived some serious fighting.
The next step is to build and paint their rhino so they can play the role in the game that I have in my head of a fast moving, hard hitting unit that is versatile enough to be used in different capacities as the mission dictates.