Wiktionary
n. (context figuratively idiomatic English) Something that generates much profit or gives great advantages.
Wikipedia
"The Golden Goose" is a fairy tale collected by the Brothers Grimm (Tale 64).
Usage examples of "golden goose".
Sturgeon led the boys in a sprint for the highway while Golden Goose ran around the east lawn, waking up all the movie people.
They would also pay well for the news that their golden goose was threatened.
Upon inquiry of the clerk laboring in the office, we were directed across the street to the sign of the Golden Goose, wherein the Sergeant might presently be found at his luncheon.
The golden goose would fly north, but in the arrival of General Calvet the Cardinal saw a heaven-sent way of preventing that flight.
The owner of the golden goose must have lived under considerable strain.
In fact, he declared (glaring at me with his shelled eyes) the Administration was bleeding the golden goose to death, and thus cooking its own.