New Delhi, June 12 -- As billionaire Elon Musk's firm SpaceX embarks on what could be the biggest initial public offering (IPO) in history, he has now become a trillionaire.

That level of wealth, owned by just one person, was previously unfathomable. Before Friday, the trillion-dollar mark was reserved only for measures like gross domestic product (GDP) or the 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 as a potential trillionaire comes amid a wider surge in wealth among the world's richest individuals. Over the year, the ranks of billionaires have continued to expand, from tech titans to celebrities. At the...