Billy Yank is the personification of the Northern states of the United States, or less generally, the Union during the American Civil War. The latter part of his name is derived from yankee, a slang term for New Englanders. Political cartoonists used Billy Yank and his Confederate counterpart Johnny Reb to symbolize the combatants in the American Civil War of the 1860s.
Billy Yank is usually pictured wearing a regulation Yankee wool uniform that included the fatigue blouse, a light-weight wool coat with an inside pocket and four brass buttons on the front, with a forage cap made of wool broadcloth with a rounded, flat top, cotton lining, and leather visor.
In the DC Comics universe, the "Spirit of America" appeared first in human form as the Minuteman and then Brother Jonathan before splitting in two during the Civil War. After the war, the two halves of its essence (Johnny Reb and Billy Yank) recombined to form Uncle Sam.