Green’s Dictionary of Slang

(US) a superior or important person, whether in fact or through pretension; thus sometimes used of God; also as adj./attrib.

1856		Democratic State Journal (Sacramento) 1 Nov. 3: The professors—the high ‘Muck-a-Mucks’—tried fusion, and produced confusion.
1862		Napa County Reporter 20 Dec. 1: McGarry with his command...succeeded in capturing the Chief of the tribe and four or five of his Hi-u-muck-i-mucks.
1879		Aberdeen Eve. News 17 Sept. 4/1: Its high muck-a-muck chief, the Grand Turk.
1880		Daily Globe (St Paul, Minn.) 6 Apr. 1/3: The condition of their market is high monkey monk just as it is here.
1881		‘Bill Nye’ Bill Nye and Boomerang 13: They want to be most worthy high grand muck-a-muck of the entire ranch.
1885		Democratic Northwest (Napoleon, OH) 8 Oct. 4/5: This man Halstead is the big mucky-muck of the Republican party.
1886		Daily Telegraph (Monroe, LA) 5 Mar. 2/2: Hugh J. Campbell, of unsavoury louisiana fame, is one of he high monkey-monks [...] in organizing a State Government for Dakota.
1890		(con. 1860s) J.O. Kerbey On the War Path 161: We were [...] introduced to the High Mucky Muck who was sitting on a dais.
1894		Anaconda Standard (Mont.) 24 Dec. 8/2: George H. Casey [...] still claims to be the high monkey monk of the board of trade.
1898		W.A. Sun. Times (Perth) 9 Jan. 7/4: A meeting of the Most Exalted and sublime Order of Hereditary Grand Muc-a-mucs was held at the High Convivial Temple.
1903		Colored American (DC) 25 Apr. 12/2: Why is that our so-called high muck-a-muck chruch people do not take stock on such things?
1904		Salt Lake Herald (UT) 12 June 6/3: He kept it up for years until he was the King / High monkey monk among us.
1905		‘West Point Sl.’ in Howitzer (US Milit. Academy) 292–5: Lights out – A warning cry, signifying the approach of some high muck-a-muck.
1906		C. M’Govern Sarjint Larry an’ Frinds 19: A Moro High Mucky-Muck never gave a man anniething out of his private boie box unless he means it as a tremendjus honor.
1912		Day Book (Chicago) 23 Oct. 4/1: A high monkey-monk who wants office.
1918		Frank L. Packard ‘Coogan’s Last Run’ in Top-Notch 1 Feb. 🌐 Be he king, prince, president, shogun, or high-mucky-muck of whatever degree.
1918		R. Lardner Treat ’Em Rough 58: And the first thing you know all the high monkey monks when they want to talk back and forth will be pageing Capt. Keefe or Major Keefe or whatever officer I am by that time.
1922		N.Y. Tribune 3 Sept. 3/6: Will Hays, high muckamuck of the movies.
1924		C.J. Dennis ‘Narcissus’ in Rose of Spadgers 154: The Lord ’Igh Muck-a-muck, wot done the trick.
1931		Shelby & Stoney Po’ Buckra 348: I always knew [...] that my boy’d get to be among the high mucky-mucks, an’ the big-bugs, an’ the bong-tongs.
1944		D. Runyon Runyon à la Carte 28: He is now a real high-muck-a-muck with the Gestapo.
1952		(con. 1920s) ‘Harry Grey’ Hoods (1953) 242: That’s the big mucky muck from the employers’ group. Anything he says that group does.
1969		‘Iceberg Slim’ Pimp 171: A lot of them are clean-cut high ‘muckty-mucks’ in the white world.
1977		(con. 1949) J.G. Dunne True Confessions (1979) 52: There was some that thought the poor man was in his dotage when he made a boy like yourself such a high monkey-monk.
1981		G.V. Higgins Rat on Fire (1982) 117: Could you embalm a high mucky-mucky-muck of the Improved Benevolent and Protective Order of Elks?
1991		Bruce Stewart Broken Arse II i: And guess who’s the highest of all—the Great Mucky-muck in the sky.