Who is the greatest man? is a question asked in the middle and end of The Adventures of Ook and Gluk: Kung-Fu Cavemen From the Future. It is repeatedly asked by Master Wong because Ook and Gluk really want the black belt. They almost always used to get it wrong, until the end of the book, when they get it right and go to save Caveland, their home town.
The question is "who is the greatest man?" and the correct answer at the end of the book is "nobody".