The U.S. dollar has become the world's largest fiat currency experiment ever. Not only is it the world's reserve currency, but numerous other nations have either adopted it as their own, used it to peg their own currency, or widely accept it to settle transactions.
Interest rates, precious metals, agricultural products, and energy are all priced in dollars.
Famously, the U.S. government pledged its support to the Saudi royal family - so long as the House of Saud accepted oil payments in "petrodollars" only.
But I'm seeing evidence that throws the dollar's long-term health and survival into doubt. I don't think it's going to disappear tomorrow, of course, but its dominance is likely on the wane.