Catapulted by the market debut of his rocket company SpaceX, Elon Musk is now the world's first trillionaire.

That level of wealth, all owned by just one person, was once unfathomable. Before Friday, the trillion-dollar mark was reserved for measures like the GDP (or staggering debt) of a handful of major economies, and, in the last decade alone, the value of some of the biggest companies to ever trade on the stock market.

Musk's new title arrives amid a wider acceleration for the richest of the rich. Year after year, his former (although now very distant) billionaires club has reaped a growing number of members,  from tech titans to celebrities. All the while, more and more people worldwide are struggling to pay their everyday bills. Many have decried the arrival of the first trillionaire as the latest and most alarming example of that wealth gap.