This position is the sort that would be called in NAmerica e.g. The Bernard Baruch Chair for Political Science at UNC. Dr Smith would be the Bernard Baruch Professor of Poly Sci.

It is a bit confusing since the word chair is also used for the chairman of the whole department, then chair is not a position, it is the person.

From your context it looks as if the chair name had been mentioned previously.

Your Inhaber... could be rendered:
the incumbent in the famous German XYZ professorship. Or, you could work the famous German in elsewhere and say Now the XYZ Professor

It's more awkward than I thought, but your context can lead you in the challenge. The URLs show this in German and English. This one shows professors in named chairs and just plain professors.

http://www.nyu.edu:81/gsas/dept/fineart/html/fct.htm

BW, Nancy