Umbragor the Hopeslayer is the highest ranking true daemon within the Brass Stampede. Ultimately subservient to Arctos Gorehowl, he is mostly left to his own devices on the battlefield. Often, this involves choosing the mightiest targets (such as Chapter Masters and Knight Titans) and hacking them apart.
The Shadows of the Hopeslayer are a numerous sect of cultists within the Brass Stampede. They paint their patchwork armor -- and occasionally their own skin -- a deep black to emulate their deity. They eagerly follow him around in battle, desperate to kill and die in his shadow. Tactically, this will usually allow Umbragor to focus on his chosen opponents while enemy troops are occupied with the tide of cultists.
His name is inspired by the character Bael'Zharon from the first generation MMORPG Asheron's Call. One of his monikers was the "Hopeslayer."
I love the GW Bloodthirster kit so much, I don't really plan on doing any conversion work for Umbragor. I'm assembling him in pieces so all appropriate surfaces can be painted without leaving unpainted spaces beneath.
I'm also magnetizing his wings for ease of storage/transport. It's a bit tricky, but I'm mostly satisfied.