Mordenkainen Presents: Monsters of the Multiverse
Consider that the duergar began as homeless outcasts, and today their fortresses are some of the most impregnable strong points in the Underdark. The question might not be if they will conquer the realm below, but when.
— Mordenkainen
Duergar are dwarves whose ancestors were transformed by centuries living in the deepest places of the Underdark. That chthonic realm is saturated with strange magical energy, and over generations, early duergar absorbed traces of it. They were further altered when mind flayers and other Aberrations invaded and performed horrific experiments on them. Fueled by Underdark magic, those experiments left early duergar with psionic powers, which have been passed down to their descendants. In time, they liberated themselves from their aberrant tyrants and forged a new life for themselves in the Underdark and beyond.
Like other dwarves, duergar are typically thick, stocky figures, though beyond this there are many differences. Both male and female duergar are typically bald, with females also lacking the capacity to grow facial hair. Many are also thinner than their dwarven brethren. Most obvious, however, was their dull gray skin and hair, often matched with an equally stolid expression. Regular dwarves claim they have flat heads, possibly as an insult.
Because many duergar found on the surface world were criminal exiles, a surface dweller who encounters one of the gray dwarves is likely to notice facial and arm tattoos that mark the duergar as a traitor to his or her people.
Tyrannical, grim, industrious and pessimistic, the lives of the gray dwarves are bleak and brutal. Rather than a flaw, however, the view their lack of happiness as their greatest strength, the defining feature of duergar pride. The duergar see themselves as the true paragons of dwarvish ideals compared to their weak and pampered kin, but in truth, their ways are merely a dark reflection of those found in normal dwarves.
While they still display the redeeming virtues of determination and bravery, duergar take dwarven flaws to their logical extremes. They are violent and hateful, sullen and insular, greedy and ungrateful, deeply cynical of others' motives and dutifully track and nurse every grudge, whether or not any offense was meant. Though their vices are many, the moral failings of the gray dwarves could be traced to three primary principles: bottomless greed, unceasing conflict, and rejection of emotion.
Most dwarves are accustomed to the inevitability of struggle to be found in existence, but such knowledge is colored by their essential love of industry. Dwarves enjoy their work, from the art of crafting to the trials of their everyday lives, seeing opportunity for success where others see labor. In contrast, duergar industriousness is spurred on simply by the primal urge to build and create, driven by a need to own and acquire as much as possible. The duergar are dauntless perfectionists who never leave a job half done and work hard to excel in their field, and yet the dwarven ideal of achieving mastery of a craft means nothing to them. Make no mistake, however, Duergar creations aren't flawed or subpar, and in fact were rather enduring. They are simply completely utilitarian, considered valuable only for their function and bereft of warmth and artistry. Appreciation of beauty has been erased from their minds, the aesthetics of their creation ignored. Their works were not labors of love, for their goal is not quality, but quantity, an attempt to craft as many items as possible as fast as possible. At the heart of duergar efforts is simple desire--an insatiable desire for wealth and prestige. Yet even when their great schemes to acquire succeed, the success is never cause for celebration, each acquisition just as incapable of satisfying their unending need for more.
The higher a duergar rises and the more items they possess, the stronger they need to be to hold on to what they already have. They are not above stealing to get their beloved gold, and by making war on others they demonstrate one of their other core principles: might makes right. The weak are unfit to possess what was meant for the strong and those too weak to defend their holdings or themselves are considered by most to be unworthy of pity. Most place little value on the lives and possessions of others, or at least their rights to these things. The helpless, weak, and those less fortunate than themselves earn little mercy, yet all-consuming envy is harbored for anyone relatively better off.