Count Strahd von Zarovich was once the conqueror of Barovia, a valley nestled deep in the Balinok Mountains. Never satisfied, Strahd made a dark bargain for utmost control over death, and both he and his lands were turned into something unholy. The lines partitioning the Prime Material were thinner in some places than others, and in such locations, Dark Powers could tempt creatures into the Deepmists. When he gave in to this temptation, mists surrounded his lands, peeling the valley away from the reality Strahd knew and into the Umbral Realms; he had become a Darklord.
Barovia became a domain of dread, a dismal place untouched by sunlight and filled with death. Its lands were inundated with Ghosts, Werewolves, and other fell creatures. Many secrets lay hidden in its Svalich Woods, including forgotten 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 the 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 it was far from the sanctuary it purported to be. The fortified village of Krezk lay near the edge of the valley, its Abbey now in the clutches of evil, misguided creatures. But of all the settlements in Strahd's domain, the Village of Barovia was by far the most oppressed. Cowering in the shadow below Castle Ravenloft and terrorized by its ageless overlord, the village's people succumbed to despair.
As adventurers traveled near the Count's domain, those bearing the Mark of Strahd watched them closely. When the time was deemed right, Strahd invited his "guests" to Castle Ravenloft, and they often became a focus of his obsession. For his own amusement, he looked to turn them against one another, torment them, and kill them. Some become his undead thralls. Some never rose again, their souls forever trapped under Barovia's heavy mists.
As long as he remained the lord of Castle Ravenloft, dawn would never come to Barovia.