it's worth understanding exactly who they are. — Xtrix 
Brett denies being interested in the question "who they are"; he says it is your question.  I've attempted to address what I thought was Brett's question, either 
who they are or how one could find out.
Here's my last attempt to explain it:
I read somewhere that most of the gold that was ever mined -- going back 3000 years -- is still in circulation. I don't know whether that is true, but it illustrates an important point: Wealth is cumulative.
The undifferentiated wealth sloshing around in the trough in 2020 has a history. You can trace the development of wealth backwards to sometime in the medieval period, probably not much before then. There are, for instance, a few companies in the world that have been in continuous existence since 1200. Some of the wealth in England goes back to grants that William the Conqueror (aka William the Bastard) made after he won the battle of Hastings in 1066. Some of the valuable land in New York City is owned by descendants of Dutch settlers before New Amsterdam became New York. Land is the original wealth. From land one can extract rent, food and fiber (like wheat and wool). England accumulated a wad of wealth by exporting fine wool to manufacturers on the continent. Later, it was coal and iron. The reason the British claimed North America was to have the land from which to extract wealth. The Germans wanted Lebensraum, and came close to getting most of Europe. Land is wealth. Nations are willing to go way out of their way to get it.
Over time, starting in the late 1700s the first industrial revolution starting up, and more wealth was created. Families who owned industrial works of various kinds became rich; their wealth was passed on in the form of investments and inheritances. Of course, sometimes big piles of wealth were lost -- someone took the land away from you; the factory burned down; one's valuable ship sank; one died without heirs, war ruined the country, and so on. But a lot of wealth moved on to other people.
The secrets of technology are another source of wealth. The British tried to hold on to the secrets of manufacturing, but as luck would have it, they failed. Americans swiped several important secrets and started up manufacturing in New England -- the beginning of the American textile fortunes.
The southern economy was devastated by the Civil War, and it took roughly a century for the southern states to recover fully. The north was enriched by the same war, and the fortunes earned (by banks, mills, railroads, farms, etc.) established a springboard to greater wealth. Metal and railroads were the leading industries after the Civil War. Andrew Carnegie was started working in 1848 at the age of 13--no huge credit to AC. Children usually were put to work early on.
Carnegie's first good job was with the Pennsylvania Railroad. He made enough money to invest in various industries and accumulated his first fortune. He started his investing about the time the civil war started. This was a period of huge growth in northern industries, and his (probably small) investments paid off hugely.
Carnegie had some money at just the right time. Had he first tried to invest shortly before the 'long depression' of 1873 which lasted 5 to 20 years, depending how one measures economic activity, he might have lost his nest egg and had difficulty recouping. Similarly, many of the people who lost a lost of wealth in 1929 didn't recover until WWII spurred huge government spending.
I’m trying to determine who they are. I don’t know why this is so difficult.
— Brett
The reason you are having so much difficulty answering the "who they are" question is that you are asking the question on a philosophy forum. What you will have to do is read history. Fortunately, that is not a dreary task. There are numerous interesting books which specifically or generally cover the question of HOW and WHO accumulated wealth from the getgo down to the present.
I am confident that you greatly exceed the necessary capacity to locate good, interesting, and economically oriented histories and read them. THEN you will know who it was that got rich and how.