[Verginius Rufus]

I think "klobucar" is the Slovenian word for "hatter." (At least it means that in Bosnian/Croatian/Serbian.)

The Mad Hatter in "Alice in Wonderland" reflects the popular belief that hatters tended to go mad.

[Calvin Locke]

... the popular belief that hatters tended to go mad.

Somebody traced it to hatters' use of mercury vapor curing felt, iirc.