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 his household. The land of the White Elephant. Siam. 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