Exclusive contracts

Not monopoly, but exclusive contracts are important.
That is, if you want it, you must buy it from me, forever.
Drug dealers.
(Andrew Carnegie)(Oops. Andrew Carnegie was steel) John Rockefeller in railroad oil transport ( he owned the patent on oil tankers) and eventually on most of the oil in the US. When they busted Standard Oil into seven smaller oil companies, each of the seven became one of the largest companies in the world.
Bill Gates on pc operating systems. He signed an exclusive contract to supply IBM with DOS, before he owned DOS. You or me, we would have said, I don't have a DOS program, but I know this guy down the valley, he has one, go see him. Bill Gates knew the guy down the valley had a DOS, and when IBM came calling, he told them he had one, and would sell it to them if they signed an exclusive contract - IBM had to buy it from him,for every pc they produced, and him alone. Then Bill went down the valley to Allen, and bought the rights to DOS from him.
The Kennedy fortune was built on an exclusive contract for Irish Whiskey imported to the US.
I should look for other examples.
Embrace your inner wolf.