Elon Musk has become the first person to cross the trillionaire threshold, at least on paper, after SpaceX priced its blockbuster initial public offering at $135 a share and its stock soared in its stock market debut.

Before the IPO, Musk was worth an estimated $813 billion, a fortune more than twice as large as the planet's second-richest person, Google co-founder Larry Page, who is worth an estimated $288 billion, according to Forbes. 

"SpaceX wants to be able to take you to the Moon, take you to Mars and ultimately beyond," Musk said at a launch event with staffers on Friday at the company's headquarters in Starbase, Texas.

SpaceX formally setting its stock price at $135 boosted Musk's fortune to just over $1 trillion. The shares, which trade under the ticker symbol SPCX, jumped after they began trading shortly before noon ET. At its closing price of $160.95 on Friday, Musk's net worth reached roughly $1.14 trillion, although future declines could push him back below the trillionaire mark.

While billionaire wealth alone may be hard enough to comprehend, a trillionaire represents a level of wealth that rivals the economic output of the world's biggest nations. Only 19 countries have GDPs that surpass $1 trillion, ranging from the U.S. to the Netherlands, according to World Bank data.

Musk's surging fortune represents a "new Gilded Age" of wealth inequality, Oxfam America senior director of economic justice Nabil Ahmed said in a statement.  

"Elon Musk's rise to trillionaire status marks a new pinnacle of oligarchy," Ahmed said. 

To be sure, plenty of other SpaceX employees and investors are likely to mint new fortunes with the IPO. About 4,400 SpaceX workers could become millionaires when the stock begins trading, according to the New York Times. But Musk is likely to be the biggest beneficiary, given his large stake in the business.

Trillionaire math

Musk owns 4.8 billion shares of SpaceX, or about 42% of the company, as well as 350 million stock options exercisable at $8.39 per share, according to the company's IPO filing. At $135 a share, Musk's stake is worth $648 billion. His options add another $44.3 billion to his net worth. 

Because Forbes valued Musk's pre-IPO stake in SpaceX at $500 billion, the IPO sale boosts the value of his SpaceX shares by an additional $192.3 billion, bringing his total net worth to $1.005 trillion. 

SpaceX shares touched as high as $168.75 in Friday afternoon trading before closing at $160.95. At the closing price, Musk's stake in SpaceX is worth an additional $326 billion, placing his total wealth at roughly $1.14 billion.

That wealth makes Musk richer than the bottom 46% of the world's population, or a combined 3.8 billion people, Oxfam said.