Barks' commentaries:

In the rough world of commerce, financial tycoons are always winning or losing monopolies on oil or rubber or something. Some even win monopolies on monopolies, and such tycoons become very, very rich. For many years Uncle Scrooge thought he had a permanent monopoly on the title 'World's Richest'. He got that way by being outrageously stingy, overbearingly aggressive, and undignified greedy. He never dreamed that another person in all the world would develop similar mastery of such an array of unsavory characteristics.
He meets such a person in this accounting of a titanic showdown in which he matches monopoly for monopoly with a master tightwad who has all of Uncle Scrooge's talents plus a little bit more. This guy is meaner, and that helps make the difference when the second-richest duck is crowned in a ruthless matchathon that dirties a strip of Africa from the Limpopo halfway to the Blue Nile.

Striving to find a duplicate for Uncle Scrooge, to show that there were other people just as ornery as he is, I invented Flintheart Glomgold, who is even more ornery than Scrooge. He takes unfair advantage of Scrooge to such an extent that Scrooge comes out being the sympathetic one. Some funny things in the story are the stinginess of those guys and the dirty things that they do to one another to save a penny. Also funny is rolling the balls of string through the heart of Africa to see which one had the most string. I don't know at what point I thought of that, but it must have been quite early in the formation of the synopsis, because I wouldn't have started out with that string-saving gag unless I had planned to use the unrolling scene. That led into action gags and comic menaces in Africa.

Years ago, saving tinfoil and string used to be quite a thing. The only tinfoil you ever came across was around chewing gum or inside of cigarette packages. It wasn't as common as it is now. People who saved tinfoil would get a ball maybe six inches across and feel quite rich. I don't know what they ever did with it - whether they really thought it had value - but it was something heavy.
People saved string back then because it was a good idea to save it. When I was a kid, you didn't get stuff in a paper bag. When you bought potatoes, the wrapping paper was folded around and tied with a string. So we always accumulated string around the house. We didn't have Scotch tape, so we used string for holding things together. Some people carried it to the point of seeing how big a ball of string they could accumulate. One old photographer had a ball over a foot across. He had been at it for years to get one that big. He couldn't explain any other reason for it except that he got satisfaction seeing how much bigger it had gotten. That's no crazier than collecting comic books...