Count Strahd von Zarovich was once the conqueror of Barovia, a valley nestled deep in the Balinok Mountains. Unsatisfied with mere rulership of his lands, Strahd made a dark bargain for utmost control. A Dark Power responded to his plea, and both he and his valley were turned into something unholy. When the pact was sealed, mists peeled Barovia away from the Material Realm into the Deepmists, and Strahd was turned into its Darklord.
Now a demiplane of dread, Barovia was untouched by sunlight and filled with death. Its dismal lands were inundated with Undead, Lycanthropes, and other fell, causing its citizens to fear the once-safe Old Svalich Road. Many secrets were lost in the Svalich Woods, including the ancient ruins and battlefields that held the story of Count Strahd's life as a conqueror. Those adventurous enough to brave the wilds could find discarded relics and forgotten remnants of Strahd's ancient enemies, though not all his foes were as dead as one might expect.
For the people of Barovia, hemmed in by impenetrable mists, there was no escape from the harsh world he created. The town of Vallaki stood ready to defend itself against the servants of Strahd, but was far from the secure sanctuary it purported to be. The fortified village of Krezk lay near the edge of the valley, hostile to outsiders, and its Abbey were held in the clutches of evil, misguided creatures. But of all the settlements in Strahd's domain, the Village of Barovia was the most affected by Strahd's bargain. Cowering in the shadow below Castle Ravenloft and terrorized by its ageless Vampire overlord, generations of the village's populace had completely succumbed to despair.
As part of his dark pact, Strahd allowed Adventurers to occasionally enter his domain, watched closely by those bearing the Mark of Strahd. When the time was deemed right, the Count would invite his "guests" to dine with him at Castle Ravenloft, and for a time, they would become a focus of his obsession. For his own amusement, the vampire turned them against one another, tormented them, and killed them. Those who did not become his thralls would never rise again, their souls forever trapped under Barovia's heavy mists.
As long as Strahd von Zarovich remained the lord of Ravenloft, dawn would never come to Barovia.