Who They Were/Are

Khazan was (or is) an archmage of considerable power who lived in Barovia. His fate remains unknown to the party.

What the Party Knows

From Victor Vallakovich in Session 13, the party learned:

Victor found Khazan’s spellbook in the Vallakovich Manor library several years ago
The Baron never noticed it was missing
The spellbook bears Khazan’s personal sigil on its cover: an intricate symbol combining arcane elements
Victor has been using it to teach himself magic, since his father refused to hire him a proper tutor
The spellbook contains advanced magical knowledge, including information about the Ethereal Plane

The platinum ring found at the site of Arabelle’s abduction bears the same sigil as Khazan’s spellbook:

Two intertwined symbols representing necromancy and evocation schools of magic
Kasimir Velikov identified the magical schools but couldn’t identify whose sigil it was
The ring’s presence at the crime scene suggests whoever abducted Arabelle may be connected to Khazan or his works

Victor revealed that Khazan built a wizard’s tower on Lake Baratok, west of Vallaki:

The tower sits at the end of a gravel causeway extending into the lake
Khazan imbued it with powerful enchantments
Most notably, the tower has a protective field that prevents other spellcasters from using magic within its influence
This anti-magic security measure makes the tower incredibly difficult to breach
Victor has asked the party to explore the tower and bring back any magical artifacts or tomes they find

Victor has access to at least one book authored by or belonging to Khazan:

Ethereal Entities: Denizens of the Unseen Realm - Contains a ritual that can temporarily transport living creatures into the Ethereal Plane
The ritual requires a night hag’s heartstone and must be performed on the night of the full moon

Khazan’s magical knowledge and artifacts have become central to multiple mysteries:

Session 13 — Victor Vallakovich revealed Khazan’s spellbook and explained about the tower on Lake Baratok
Session 13 — Victor explained that Khazan’s books contain the ritual needed to enter the Ethereal Plane