Why is it der Bonner?

Bonner ends in -er, and most nouns ending in -er are masculine: in a German dictionary, 86% of them take der.

All nouns ending in -er
Sense 1
der

Meaning

[1] A resident, resident of the city of Bonn, a person born in Bonn

[1] ein Einwohner, Bewohner der Stadt Bonn, eine in Bonn geborene Person

Examples

[1] I am born in Bonne

[1] Ich bin gebürtiger Bonner.

Declension

1 Singular Plural
Nominativ der Bonner die Bonner
Genitiv des Bonners der Bonner
Dativ dem Bonner den Bonnern
Akkusativ den Bonner die Bonner

Pronunciation

Dictionary entries include material from Wiktionary. Wiktionary