Green’s Dictionary of Slang

(orig. US) any successful, wealthy, influential person; recent UK use has tended to imply a degree of self-serving corruption to such individuals; thus also as v.

[1904		Sun. Times (Perth) 20 Mar. 8/2: Watson [...] is one of the fattest of guinea-pigs drawing a good income from insurance and other companies for the untiring work of doing nothing].
1925		Denton (MD) Journal 7 Nov. n.p.: The Republican party promises the finest fat cat fight ever seen in this State [...] It ought perhaps to be explained that fat cat is the significant and revealing name [...] as candidate or backer, the magic words ‘fat cat’ ring throughout the wards [...] Soon or late every fat cat in the party will likely be involved.
1931		C.B. Yorke ‘Mob Murder’ in Gangland Stories Mar. 🌐 ‘Mark Sands is the Big Shot—State senator and biggest fat cat in politics.’.
1946		H. Boyle 8 Jan. [AP synd. article] ‘Fat-catting’ is a term applied in the lower ranks to high leaders who try to guide their military personal careers back into the easy pre-war days of Colonel Blimp by padding themslves with special privileges and comforts.
1955		B. Schulberg On the Waterfront (1964) 315: The new Fat Cat was known as Smiling Matt Bailey.
1969		N. Spinrad Bug Jack Barron 20: You freeze fat cats, shade fat cats.
1975		J. Wambaugh Choirboys (1976) 170: Catching Foxy Farrell blowing some fat cat in the dressing room.
1986		B. Geldof Is That It? 258: The room was full of Hollywood fat cats and their wives.
1991		D. Jarman letter 28 July Smiling in Slow Motion (2000) 43: Who gives a fuck for these fat cats who have built their careers.
2007		C. Goffard Snitch Jacket 238: She’s a fat cat [...] a big contributor to the guy running against the Orange County DA.
2011		Sun. Independent (SA) 13 Mar. 1: [headline] Fat Cats Coin It.
2012		T.P. McCauley ‘Lady Madeline’s Dive’ in ThugLit Sept./Oct. [ebook] ‘You brought those two fat cats in the tuxes here’.
2023		(con. 1962) J. Ellroy Enchanters 149: ‘He’s a big Republican fat cat!’.