Elon Musk has finally done it: turned Twitter to X.

While the unveiling of X on a Sunday caught many people unaware, it was not a surprise.

The platform's owner has talked about turning it into "X" for months, while being a bit vague about what that exactly means. Does X represent a major business experiment? A radical new concept for on-line living? Or is it simply one man's obsession with the 24th letter of the alphabet?

Probably it's all of the above.

"X," Musk tweeted in April.

A few days earlier a filing in a federal court case in California confirmed that Twitter had been folded into X Corp.

In announcing the company's new CEO, Linda Yaccarino, this May, Musk wrote on then-Twitter: "Looking forward to working with Linda to transform this platform into X, the everything app."

Yaccarino seems keen to do exactly that, posting on Sunday that "X will be the platform that can deliver, well....everything."

In some ways, the letter "X" frames everything about Musk's ambitions, according to biographers, from where he is headed to where he got his entrepreneurial start.

X.com, the bank where it began

According to Ashlee Vance, the author of Elon Musk: Tesla, SpaceX, and the Quest for a Fantastic Future, Musk's obsession with the letter X began with one of the billionaire's earliest ventures, X.com, which later merged with a competitor to become PayPal.

"Everyone tried to talk him out of naming the company that back then because of the sexual innuendos, but he really liked it and stuck with it," said Vance.

In 2017, Musk repurchased the url "X.com" from PayPal, tweeting that the domain "has great sentimental value."

X, the Tesla model

"X marks the spot in a lot of ways for Elon Musk," said Tim Higgins, a Wall Street Journal reporter and the author of Power Play: Tesla, Elon Musk, and the Bet of the Century. "It's kind of this common theme throughout."

The letter X became the name of Tesla's third model, which debuted in 2015.

"The idea being that the Tesla models would spell out the word 'sexy,'" Higgins said. But Ford owns the right to the Model E, which is why Musk later settled on the Model 3, "kind of a backwards E," he said.

X, the first letter of his youngest son's name

In 2020, Musk and his then-partner, Grimes, welcomed a son via surrogate, naming him X Æ A-12 Musk. (Æ is pronounced "ash," Musk told controversial podcast host Joe Rogan.)

The couple named their second child, a girl, Exa Dark Sideræl Musk. (It's now been changed to "Y.")

X, the everything app

But lately, "X" has referred to Musk's newest ambition, building an "everything app" akin to China's popular WeChat, which doesn't yet have a U.S.-parallel.

"He wants to create an app similar to how WeChat is used in China, where it's part of the fabric of day-to-day life. You use it to communicate, to consume news, to buy things, to pay your rent, to book appointments with your doctor and even to pay fines," said Vance.

Vance says following the WeChat model makes sense with what Musk wants for Twitter. "The company clearly needs a new, bigger business if it's to make the type of money that would justify his investment and satisfy his ambition," he said.

Weeks before he shelled out $44 billion to acquire Twitter in October, Musk tweeted, "Buying Twitter is an accelerant to creating X, the everything app."

X...?

But Musk's obsession with the letter X is still something of a mystery even to his biographers, like Higgins.

"Whether it's kind of mysterious, like something pulled from a comic book, or 'X marks the spot,' it's hard to know with him," Higgins said. "It also just kind of sounds cool."

This story was updated on July 24, 2023, by Lisa Lambert.