Why is it der Madrider?

Madrider 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] residents of the Spanish capital Madrid

[1] Einwohner der spanischen Hauptstadt Madrid

Examples

[1] He asked a Madrider for the way to the Plaza Mayorä

[1] Er fragte einen Madrider nach dem Weg zum Plaza Mayor.

Declension

1 Singular Plural
Nominativ der Madrider die Madrider
Genitiv des Madriders der Madrider
Dativ dem Madrider den Madridern
Akkusativ den Madrider die Madrider

Pronunciation

Dictionary entries include material from Wiktionary. Wiktionary