King of the White Elephant. The proudest title borne by the
kings of Ava and Siam. In Ava the white elephant bears the title of
“lord,” and has a minister of high rank to superintend
The land of the White Elephant.
To have a white elephant to keep. To have
an expensive and unprofitable dignity to support, or a pet article to
take care of. For example, a person moving is determined to keep a pet
carpet, and therefore hires his house to fit his carpet. The King of
Siam makes a present of a white elephant to such of his courtiers as
he wishes to ruin.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894
More on White Elephant from Infoplease: