Declension of German Names

So you know how and when to decline nouns and adjectives, but how about names or titles? Would you address an envelope to your boss as An Herr Stuhlinger or An Herrn Stuhlinger? The answer is the latter, since an is here in the dative. How about if his name were Doktor Stuhlinger? Then, the answer would be An Doktor Stuhlinger, even though it still remains in the dative.
Here are a few simple rules of declination to keep in mind when using names and titles:

1) Declension of Names Without Titles

Names are always invariable except when in the genitive. You can decline a name in the genitive in two different ways:

If the name is used by itself, meaning it is not accompanied by an article, possessive adjective or anything else, then an –s- will be added.

Ingrids Aufsatz (Ingrid’s essay)
Goethes Werke (Goethe’s work)
die Eltern Helmuts (Helmut’s parents)

If in the same phrase both first name and last name is used, then it is the last element that takes the –s-.

Friedrich von Schillers Werke (the work of Friedrich von Schiller)

Other important points to remember when names are not accompanied by an article, possessive adjective or anything else:

Similar to English, names ending in s,x, z, tz orβ take an apostrophe and not an s.
Moritz’ Freund heiβt Max. (Moritz’ friend is called Max.)

You can always replace the genitive with a preposition plus the dative.
Der Freund von Moritz heiβt Max. (The friend of Moritz is named Max.)

If the name is accompanied by an article, possessive adjective or other, then the name remains undeclined:

die Werke des jungen Schiller (the works of young Schiller)
die Noten unseres Sohnes Maximilian (the successes of our son Maximilian)

2) Declension of Names with Titles

If the name with a title is accompanied by an article, possessive adjective or other, it is the title that is declined and not the name. Here also, titles are only declined when in the genitive, except for Herr.(Gehört das Auto Herrn Breitbach?/ Gehört das Auto Professor Breitbach?)

Die Krone des Königs Ludwig XV (You read it as des Königs Ludwig des Fünfzehnten)

Take note: if more than one title precedes a name, then solely the first one is declined:

Das Buch der Direktorin Dr. Offenbach
Das Buch des Rektors Professor Dr. Steinle

Exception: The word Herr is always declined no matter how many titles accompany it:

When the title is not preceded by an article, then the name is declined.

die Vorlesung Professor Schmitts (the lecture of Professor Schmitt)
Das Buch Dr. Steinles

Take note: the title Doktor/ Dr. always remains undeclined.

When the title is preceeded by an article, then the title and not the name is declined.

die Vorlesung des Professors Schmitt