Green’s Dictionary of Slang

pooh-bah n.

also poo-bah, pooh-ba
[Gilbert and Sullivan’s Savoy Opera, The Mikado (1885), in which ‘Ko-Ko’ is ‘Lord High Executioner of Titipu’ and ‘Poo-Bah’ is ‘Lord High Everything Else’]

1. an important person; also attrib.

Springfield Globe-Republic (OH) 18 Apr. 6/2: Whom did we elect to that high-mighty and pooh-bah position?
[Aus]Bulletin (Sydney) 2 Aug. 11/2: J.G. Knight of the new Government Resident of the Northern Territory, is a regular Poo-bah, and is regarded as an improved Czar up that way. He has five different billets, and gets about £600 a year after twenty years’ service.
[Aus]Sun. Times (Perth) 24 June 4/6: The big-headed Poo Bah Brown, who was such a ghastly failure as Mayor of Perth.
[Aus]Truth (Melbourne) 3 Jan. 5/2: This Pooh-bah business could not, of course, yield but the rottenest results.
[UK]‘Ian Hay’ Carrying On 5: Ayling has departed [...] and rumour says he is leading a sort of Pooh Bah existence at Brigade Headqurters.
[UK]‘Sapper’ Bulldog Drummond 152: When the young Pooh-ba comes of age, naturally his devoted parent will sport her glad rags.
[Aus]Brisbane Courier 18 Aug. 6/8: In many places a policeman is a general Pooh-bah.
[US]‘Max Brand’ Pleasant Jim 11: Eight thousand you get from some damned Pooh-Bah who’ll make a speech to you and then forget you.
[US]E.R. Burroughs ‘Resurrection of Jimber-Jaw’ in Goodstone Pulps (1970) 4/2: He had been [...] stepping on the toes of the constituted medical poobahs.
[US]Lait & Mortimer USA Confidential 127: B. Kaufman, of the Sellman Hotel, is the pooh-bah of the cafes and restaurants. [Ibid.] 132: He was and is the poobah.
[US]‘Tom Pendleton’ Iron Orchard (1967) 17: Our local high Pooh-Bah is Mr. Scofield, the field superintendent.
[US]H. Rawson Dict. of Invective (1991) 308: pooh-bah. A pompous person. The epithet converts an important person into a self-important one.
[UK]Guardian Rev. 27 Nov. 1: If you happen to wake up one morning to find yourself the big Pooh-bah for your district.
[US]J. Ellroy ‘Little Sleazer & the Mail-Sex Mama’ in Destination: Morgue! (2004) 167: Sweaty Jimmy Swaggart and paralyzed pussy pooh-bah Larry Flynt.

2. someone or something that serves multiple purposes.

[US]N.Y. Tribune 16 Oct. 11/1: I learned that this wagon was a ‘Pooh Bah’ among vehicles, serving by turns as patrol wagon, amubulance and hearse.

In derivatives

pooh-bahism (n.)

the promotion of individuals on the basis of connections rather than ability.

[Aus]W.A. Sun. Times (Perth) 19 May 1/1: Poo Bah-ism is rampant in the Civil Service of this state.