What is known publicly is certainly an indication that he is criminally wealthy. I can't find the reference right now, but there's a Russian bureaucrat close to Putin that makes a small salary, yet he has a large villa in Italy and many other properties, totally many millions of <insert currency> of net worth. There was even a Russian citizen that was documenting and publishing the info and using drones to video him at his Italian villa. I wish I could find that link, it was fascinating.

Ah, found it:

https://www.nytimes.com/2017/03/02/world/europe/russia-dmitr...

The video, with English subtitles, as almost 24M views:

https://www.youtube.com/watch?v=qrwlk7_GF9g