Gyllenhaal is a Swedish noble family descended from the cavalry Lieutenant Nils Gunnarsson Haal (d. 1680 or 1681), ennobled in 1652 with a change of surname to Gyllenhaal. Some notable members of this family are:
Nils Gunnarsson Gyllenhaal's descendants today stem from two of his sons; Lars Gyllenhaal b. 1645 d. 1710, Lieutenant of the Vestgotha cavalry regiment, and his younger brother Hans Gyllenhaal b. 1655 d. 1710. Hans was killed in action at the battle of Helsingborg as a cavalry captain.
The members of the older branch descending from Lars are still living in Sweden. The most notable member of that branch is the above mentioned Prime Minister for Justice Lars Herman Gyllenhaal. In 1851 he was created Knight and Commander of the Royal Order of the Seraphim. His great-great grandson Herman Gyllenhaal till Haerlingstorp b. 1934, is now the baron of the family and his son, the above-mentioned Lars Gyllenhaal, is now the head of both branches of the noble family Gyllenhaal.
All the members of the family in the USA are descending from Hans Gyllenhaal and come from his great great-great grandson Anders Leonard b.1842 d. 1905, who in 1866 immigrated to the USA, and his wife Amanda b. Nelson b.1859 d.1948. The hitherto most memorable member of this younger branch was the above-mentioned *Leonard Gyllenhaal (1752-1840). He was in 1807 created a Knight of the Royal Order of Vasa for his scientific works as an entomologist and his scientific work about Swedish insects, Insecta Suecia descripta.
The spelling of the name Gyllenhaal caused problems right from the beginning. Its origin is clear: Nils Gunnarsson Gyllenhaal's father was Gunne Olofsson Haal from Hahlegården, a crown homestead in South Härene Parish in the county of Västergötland in West Sweden. Here you see both the explanation and the problem; "Haal" comes from the name of the farm "Hahlegården", "only" the spelling is different. This confusion was mirrored in Nils' ennoblement: In the Knighthood Letter, signed by Queen Christina, the family name was written in two different ways- first "Gyllenhahl" and then "Gyllenhaal". On the copperplate with his coat of arms now hanging in the House of Nobles (Riddarhuset) in Stockholm it is spelled "Gyllenhahl". See www.gyllenhaal.org. The prefix "Gyllen", i.e. "Golden", was the one most used when ennobling someone since the 16th century (cf. the former head of the car manufacturer Volvo Pehr Gustaf Gyllenhammar and Sofia De la Gardie).
Jake Gyllenhaal, great-great grandson of the above-mentioned Anders Leonard Gyllenhaal, joked to an interviewer, in connection with the British première of the movie Prince of Persia in May 2010, that his last name was pronounced "Yil-en-hoo-luh-hay", poking fun at Swedish pronunciation.
Difficulties with the pronunciation of "Gyllenhaal" are, however, not new. In the Scandinavian languages a double "aa" as in Gyllenhaal, has for centuries normally been pronounced with an "o" sound as in English "for". In this case, however, in Swedish it is pronounced with a long "a" as in the English word "far"; the double "aa", as with the "ah" in the alternative "Gyllenhahl" (see above) only indicates a long vowel "a".
The second problem for English-speakers is how to pronounce the prefix "Gyllen", i.e. Golden. The family branch in USA has solved it with pronouncing it "Jill-EN-hall", but in Sweden the letter "y" is pronounced as a close front rounded vowel, similarly to the German vowel "ü".