Green’s Dictionary of Slang

something very important of its type.

1835		D. Crockett Col. Crockett’s Tour to North and Down East 37: We soon came in sight of the great city of New York, and a bulger of a place it is.
1848		Bartlett Dict. Americanisms.
1859		Hotten Dict. of Modern Sl. etc. 13: bulger, large; synonymous with buster.
1860		Hotten Dict. of Modern Sl. etc. [as cit. 1859].
1872		Schele De Vere Americanisms 587: Bulger, from to bulge (French bouger), to swell out, is hence literally a swell, but in the United States generally designates anything very large. ‘That’s a bulger of a story.’.
1890		Music Hall & Theatre Rev. 8 Feb. 6/2: Dodo [...] and his terrible man-eating dog, Bulger, and you can bet he is a bulger.