The Umbragen are a cultural offshoot of the Xen'drik Drow, who fled into Khyber to escape the Scouring of Xen'drik. Khyber was full of terrors, but it was nevertheless preferable to the apocalypse happening on the surface as the Giants and the Dragons fought. Eventually, these refugees found their way into a demiplane beneath the Ring of Storms, Taer Umbra. Within, they found an abandoned fortress that once belonged to the Qabalrin, a culture of Elves that once rivalled the empires of the giants before their destruction.
The Qabalrin were long gone when the drow found their outpost, but their works and texts remained. The drow found a set of texts that described a vast well of spiritual energy, a force the ancient elves called The Umbra, as well as the means to tap into it. The drow, beset upon by horrors and struggling to adapt to life underground, made a pact with the Umbra to save them. Over the course of generations, this pact has physically changed the drow, manifesting shadowy marks on their skin and turning their eyes into wells of darkness. These drow now refer to themselves as the Umbragen.
The Umbragen believe that using the power of the Umbra erodes the soul, as the Umbra is a force of entropy. Those who use the power frequently become colder and more ruthless, their empathy eroding as their power grows. They are aware of this, and those who choose to do so make the sacrifice willingly to help them protect their home. An outside observer might come to the conclusion that they worship The Shadow, but they have no knowledge of the Sovereign Host.
The Umbragen never know peace, as they are constantly under attack from the denizens of Khyber. Most recently, and most tenaciously, the Umbragen have been at war with the forces of Belashyrra, the Lord of Eyes. It is a vicious struggle, one that drives the drow even deeper into the clutches of the Umbra to survive, but so far they have managed to keep the forces of the Daelkyr at bay.
Recently, the Umbragen have begun sending forces to the surface and to other demiplanes, searching for allies or knowledge that can help them in the Blind War.