der Luxemburger
Luxembourger
A male resident of Luxembourg or a male person of Luxembourgish origin.
Der neue EU-Kommissar ist Luxemburger.
The new EU commissioner is a Luxembourger.

Luxembourger
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Luxembourger
A male resident of Luxembourg or a male person of Luxembourgish origin.
Der neue EU-Kommissar ist Luxemburger.
The new EU commissioner is a Luxembourger.

Male names for residents of countries and many cities are often formed in German with the ending '-er'. 'Luxemburger' follows this pattern, just like 'Berliner' or 'Wiener'.
Mein Kollege ist gebürtiger Luxemburger.
My colleague is a native Luxembourger.
Words like 'Luxemburger' are nouns and are always capitalized. They are declined like normal nouns and can be used with an article.
Ich habe gestern einen Luxemburger kennengelernt.
I met a Luxembourger yesterday.
The noun 'Luxemburger' refers only to people. To describe the origin of things or abstract concepts, the adjective 'luxemburgisch' (Luxembourgish) is used.
Das ist ein typisch luxemburgisches Gericht.
That is a typical Luxembourgish dish.