How the Spencer jacket came about is a matter of dispute. The jacket was named for George John Spencer, the second Earl of Spencer (1758-1834). One belief is that the earl was thrown from his horse and tore his long-tailed riding coat on a thorn bush. Spencer conceived the idea of a short coat that would not be damaged in such circumstances. At that time, only a coat with tails was considered proper dress.
Another belief is that the earl wagered that he could set a new fashion by wearing a short overcoat without skirts, which he wore as he strolled the streets of London. Spencer won the bet. The jacket gained immediate popularity; it became quite stylish, de rigueur among the social elite.
The name came to be applied also to a close-fitting bodice for women, but there the word’s lineage is clearer: It was designed by a Mr. Knight Spencer.