Short answers, pulled from the story.
Tracy and Laura Hickman created Strahd von Zarovich and the Ravenloft setting, developing the idea under the working title Vampyr before TSR hired them to adapt it into the first edition of Advanced Dungeons & Dragons, released as Module I6: Ravenloft in 1983.
The Demiplane of Dread is Ravenloft's pocket-dimension setting, made up of land pieces called domains held together by a mysterious force called the Dark Powers. Each domain is ruled and mystically imprisoned by a Darklord, surrounded by magical mists that cannot be crossed.
Vecna and Lord Soth are the only two Darklords known to have escaped Ravenloft. Vecna escaped by becoming a Greater God, too powerful for the Dark Powers to contain, and Lord Soth escaped after the Dark Powers lost interest in his punishment.
Ravenloft has been criticized for reinforcing harmful stereotypes through the Vistani, its in-fiction stand-in for the Romani people. Wizards of the Coast revised the depiction in Curse of Strahd: Revamped (2020) and Van Richten's Guide to Ravenloft (2021) with input from a Romani consultant, though critics such as Julie Muncy and Jon Ryan argued the changes remained limited.
Ravenloft first appeared in 1983 as Module I6: Ravenloft, a stand-alone Advanced Dungeons & Dragons adventure published by TSR. It won the Strategists' Club Award for Outstanding Play Aid the following year, in 1984.
Wizards of the Coast's Season of Horror, announced in March 2026 and beginning in June 2026, brings the 5.5 Edition sourcebook Ravenloft: The Horrors Within, detailing sixteen Domains of Dread including the new cosmic horror domain Innsmouth. It also includes the Horrified: Dungeons & Dragons - Ravenloft board game and a new comic series starting on the 19th of August 2026.