Dr. Rudolph Van Richten
was a Vampire
hunter whose family was lost due to them. He appears in many Ravenloft modules and has written several books about its inhabitants.
In the most recent Ravenloft module Curse of Strahd, he traveled to Barovia to kill Strahd disguised as the Half-Elf bard Rictavio (Below). He used Khazan's tower as a hideout.
He can be found at the Blue Water Inn in Vallaki.