Anonymous reviewer disclosed his identity. Should I thank him by name? A "friendly" reviewer purposely disclosed his identity to me (the author) during a previous round of reviews of a paper that was not published back then. However, he helped me to make the article better. If I publish the paper now, should I thank him by name or as an anonymous reviewer?
You can thank him by name for making helpful suggestions for improvement. You don't need to say that the comments were during a formal review. 

Alternatively, he should be thanked as an anonymous reviewer. 

I would, personally, prefer the first alternative. The publisher might also prefer it if you are using the name.