With the members of the Third legion and their allies spread through out swathes of books it can at times be quite a task to hunt down the descriptions of them, be it for art, conversions/kitbashes, lore discussions or any number of things. As such my hope with this thread is to make things a bit easier for fellow fans of the legion looking for such details.
This thread shall cover the The Forces of the Lord Commander Primus.
Lord Commander Eidolon

Galaxy in Flames-
Eidolon carried a powerful natural authority about him, accentuated by magnificent armour with such an overabundance of gilding that the purple colours of the Legion were barely visible. A second delegation arrived through another of the arches, arrayed in the purple and gold of the Emperor's Children. Led by Eidolon in all his magnificence, a squad of Astartes with glittering swords marched alongside the lord commander, their battle gear as ornate as their leader's. Tarvitz saw the golden armour of Eidolon flashing in the planet's hard light, the lord commander hefting a mighty hammer with blue arcs of energy crackling around its head. The hammer slammed into die remains of the doors, blue-white light bursting like a lightning strike as they vanished in a thunderous explosion.
Eidolon was on his knees, his hammer lost and the Warsinger hovering over him. Her hands stretched out in front of her as she battered Eidolon with waves of force strong enough to distort the air. Eidolon's armour warped around him, his helmet ripped from his head in a wash of blood, but he was still alive and fighting. Eidolon's eyes were ablaze, his hatred and revulsion at this foe clear as his mouth opened in a cry of rage. His mouth opened still wider and he let loose his own screeching howl. Eidolon bent and picked up Tarvitz's fallen broadsword, his own terrible scream now silenced. Eidolon looked up at the statue towering over them, the hollow eyes regarding them with a cold, unflinching gaze.
Reflection Crack'd -
Eidolon’s skin was waxy and pale, pulled tightly across the distended orbits of his eyes. Wire-taut tendons throbbed at his neck, and the bones of his lower jaw moved with the liquid detachment of a serpent. His armour was painted in garish stripes of vivid purple and electric blue, the colours riotously applied in a striking pattern that owed nothing to any design of camouflage and made Lucius’s eyes strain to assimilate what he was seeing. Such vivid colourings were now the norm among the Legion, with each warrior striving to outdo his fellows in sheer extravagance and ostentation.
Eidolon laughed, the gesture opening his face up like a tearing wound. He crashed down into the rubble left by the demolition of the tiered benches, his breastplate cracked wide and his taut skin spattered with blood. The quillons of Eidolon’s sword had barely parted company with the lip of his scabbard when the anathame cut through his neck and sent his head flying through the air. It landed with a meaty thud on the terrazzo floor and rolled until it finally came to rest against one of the urns of victory wine. The Lord Commander’s eyes blinked once, his lips drawn back over his splintered teeth in an expression of horror that made Lucius want to laugh.
This thread shall cover the The Forces of the Lord Commander Primus.
Lord Commander Eidolon

Galaxy in Flames-
Eidolon carried a powerful natural authority about him, accentuated by magnificent armour with such an overabundance of gilding that the purple colours of the Legion were barely visible. A second delegation arrived through another of the arches, arrayed in the purple and gold of the Emperor's Children. Led by Eidolon in all his magnificence, a squad of Astartes with glittering swords marched alongside the lord commander, their battle gear as ornate as their leader's. Tarvitz saw the golden armour of Eidolon flashing in the planet's hard light, the lord commander hefting a mighty hammer with blue arcs of energy crackling around its head. The hammer slammed into die remains of the doors, blue-white light bursting like a lightning strike as they vanished in a thunderous explosion.
Eidolon was on his knees, his hammer lost and the Warsinger hovering over him. Her hands stretched out in front of her as she battered Eidolon with waves of force strong enough to distort the air. Eidolon's armour warped around him, his helmet ripped from his head in a wash of blood, but he was still alive and fighting. Eidolon's eyes were ablaze, his hatred and revulsion at this foe clear as his mouth opened in a cry of rage. His mouth opened still wider and he let loose his own screeching howl. Eidolon bent and picked up Tarvitz's fallen broadsword, his own terrible scream now silenced. Eidolon looked up at the statue towering over them, the hollow eyes regarding them with a cold, unflinching gaze.
Reflection Crack'd -
Eidolon’s skin was waxy and pale, pulled tightly across the distended orbits of his eyes. Wire-taut tendons throbbed at his neck, and the bones of his lower jaw moved with the liquid detachment of a serpent. His armour was painted in garish stripes of vivid purple and electric blue, the colours riotously applied in a striking pattern that owed nothing to any design of camouflage and made Lucius’s eyes strain to assimilate what he was seeing. Such vivid colourings were now the norm among the Legion, with each warrior striving to outdo his fellows in sheer extravagance and ostentation.
Eidolon laughed, the gesture opening his face up like a tearing wound. He crashed down into the rubble left by the demolition of the tiered benches, his breastplate cracked wide and his taut skin spattered with blood. The quillons of Eidolon’s sword had barely parted company with the lip of his scabbard when the anathame cut through his neck and sent his head flying through the air. It landed with a meaty thud on the terrazzo floor and rolled until it finally came to rest against one of the urns of victory wine. The Lord Commander’s eyes blinked once, his lips drawn back over his splintered teeth in an expression of horror that made Lucius want to laugh.