In Curse Of Strahd, the Heralds of Dawn found Nikolai's undead body in Fiona's bed while raiding the Wachterhaus. They used this as testimony against Fiona's character in the Silver Dawn Of Vallaki, and after the trial, he was finally let to rest. Surrounded by family, they removed the copper pieces from his eyes, and he started to rot. After the revolution, he was buried in Saint Andral's Church.
Born Nikolai Olegovich to a rich family in Vallaki, Nikolai wed Fiona Wachter and adopted the Wachter family name at 23. With his wife, he eventually sired Nikolai II, Karl, and Stella, and grew the Wachterhaus's influence into becoming an incredibly powerful noble house in the region, second only to the ruling Vallakovich.
Known for his charisma, intelligence, and caring nature, Nikolai was well-loved both among his family and his peers. However, he was weak of body, and battled sickness all throughout his life. He fell deathly ill and eventually passed away, causing a major shift in his wife's personality. She began distancing herself from family matters and focused purely on acquiring the power needed to make the Wachter family rule Vallaki.
Unknown to outsiders and even her own children, Fiona remained absolutely obsessed with her husband after his death. She kept him in her bed under the effects of a gentle repose Spell; copper pieces over his eyes, impeccably dressed, and quite deceased.