In ancient legend, there are types of swans that either sing most beautifully when they are dying or never sing until just before death. Despite being untrue, the legend has survived from antiquity into modern times, probably because it lends itself so well to poetic allegory. Today it lives on primarily in the idiom swan song (sometimes swan-song), which refers to the last performance or work by someone who is retiring or dying. A swan song isn’t necessarily the greatest work of one’s career, but it is seen to have extra significance, especially if its creator produces it knowing it is to be his or her last work.
This was the last effusion, the swan-song of Denis, who died on the 29th of September, 1800. [Historic Survey of German Poetry, William Taylor (1830)]
The song which was denied to him in his life-time, had become his swan-song, which was softly to unloose his limbs and dissolve him in death. [The Churchman's monthly magazine (1857)]
The others on trial, led by Goring, whose weight had tumbled from 264 pounds to a mere 187, sang Nazism’s swan song to the end. [Life (1946)]
And I definitely do intend to finish with it as soon as I’ve written by last work—my swan song. [Fantastic Stories, Abram Terts (1987)]
With Mr Greenspan expected to step down in January, two months before his 80th birthday, this may be his swan-song before the legislative body. [Economist (2005)]
Misty May-Treanor and Kerry Walsh Jennings took their third straight Olympic gold medal in their swan song as a beach volleyball duo. [Los Angeles Times (2012)]