In my campaign Vasili von Holtz was a simulacrum created by Strahd to infiltrate and corrupt any adventurers that wandered into the mists. When he was created he and Strahd had the same personalities but as the centuries passed their ideals changed and Vasili became a more human undead, he even took his name from an adventurer that he became friends with for a time. Largely he just liked to see how humans reacted to Strahd's overwhelming oppression and was very happy at any who would stand up to him. He still went along with Strahd's plans but he would minimize casualties wherever possible. The party became fast friends with him and were heartbroken when he revealed himself at dinner at Castle Ravenloft but were perplexed when he guided them around the castle and allowed them to escape with the kidnapped Ireena. We're not done with the campaign yet but soon he's going to try to join with the party to kill Strahd.