Grand Poobah is a contemptuous expression used for overly self-important people, who hold a ridiculously large amount of public offices and titles.
The term is especially encountered in the TV cartoon The Flintstones.
The humorous title was created from the name of a character in the 1885 comic opera by W. S. Gilbert and Arthur Sullivan, titled The Mikado.
The character, Pooh-Bah is remembered for having an abnormally large list of titles to his name.
The components of his name, pooh and bah are both words for expressing contempt toward something negative.
The term, “Grand Poobah” had been created and adopted into everyday language, after the success of the opera.
It got further embedded into the lingo in the 1960’s TV cartoon, The Flintstones, in which the two protagonists, Fred Flintstone and Barney Rubble are both members of a secret society, called The Loyal Order of Water Buffaloes, referencing real life secret lodges, like the Freemasons and the Moose Lodge.
The phrase was first defined on Urban Dictionary in 2006, with a couple of other entries being written on “Grand Poobah” since then.