"The English name wren derives from Middle English wrenne, Old English wraenna, attested (as werna) very early, in an 8th century gloss. It is cognate to Old High German wrendo, wrendilo and Icelandic rindill (the latter two including an additional diminutive -ilan suffix). The Icelandic name is attested in Old Icelandic (Eddaic) rindilþvari. This points to a Common Germanic name *wrandjan-, but the further etymology of the name is unknown.
The wren is also known as kuningilin "kinglet" in Old High German, a name associated with the fable of the election of the "king of birds". The bird who could fly to the highest altitude would be made king. The eagle outflew all other birds, but he was beaten by a small bird who had hidden in his plumage. This fable is already known to Aristotle (Hist. animalium 9.11) and Plinius (Naturalis hist. 10.74 ), and was taken up by medieval authors such as Johann Geiler von Kaisersberg, but it concerns Regulus, and is apparently motivated by the yellow "crown" sported by these birds (a point noted already by Ludwig Uhland). In modern German the name is "Zaunkönig", king of the fence (or hedge). In Dutch the name is "winterkoninkje" (little winter king)." source: wikipedia