Biography
Hans Detlef Sierck was born in Hamburg on April 26, 1897 to Danish parents.  Sierck married Lydia Brinken, an actress, and had a son, Claus Detlef.  A few years later, Sierk and Brinken divorced.  Brinken, who later became a Nazi, obtained a court order barring her ex-husband from seeing Claus on the grounds that Sierk's second wife, Hilde Jary, was Jewish.  After that point, Sierk was never again allowed to see or talk to his son.  Sierk's son died in the spring of 1944 on the Russian front fighting as a Nazi.  The 
tragic events of this father/son relationship haunted him so much so that Sierk later used the experience as inspiration for the 1958 film A Time to Love and a Time to Die.

In the late thirties, Sierk, a man of the left with a personal distaste for Hitler himself, fled his native Germany in opposition to the Third Reich. Sierk moved to America where, under the strong advice of his agent, he changed his name to Douglas Sirk.

Sirk had a long theatrical history in Germany.  He was also an acclaimed director in Germany. (For an extensive filmlist, go
here.) Sirk's subsequent American career was marked by his signature melodramas such as Magnificent Obsession and Imitation of Life. As Leonard Maltin said, "While the films might well collapse under such intellectual baggage, it is well known that Sirk was a cultivated, aesthetically advanced man who brought more to such projects than they might have "deserved."" (1994)

During its release,
Imitation of Life became Universal's most commercially successful picture. It also proved to be Sirk's last film. After this movie, Sirk retired from filmmaking and returned to Europe, living in Switzerland and Germany until his death in January of 1987.
 
To those that knew Sirk, he was considered thoughtful, impressive, and very well-read.  "He was tremendously funny, wonderful company, with a mind that was deep and unusual.  He relished dark humour, and playfulness, not least with language.  Just as his films could conjure drama, magic, and despair out of apparently humdrum, everyday situations, he could invest every topic of conversation with excitement and knowledge."
(3)