When Larry Ellison entered his ninth decade in 2024, his high-profile lifestyle seemed to be receding. The future promised fewer thrilling yacht races and mock dogfights over the Pacific and more legacy-securing philanthropic gestures. Software moguls get old, too.

Instead, in a remarkable new chapter, even by the standards of the truly rich, Mr. Ellison has suddenly decided to become a media magnate, one whose portfolio and power could exceed those of fabled predecessors like Hearst and Pulitzer.

Oracle, the tech company Mr. Ellison co-founded and still controls after nearly half a century, is among the investors in the newly formulated American version of TikTok, the short video app that claims 170 million U.S. users. Mr. Ellison owns more than 40 percent of Oracle’s stock and is its chief technology officer.

Many elements of the new TikTok remain unclear, including the exact ownership shares and who will run the company. About the only safe assumption is that the app will be controlled by people sympathetic to President Trump. The Murdoch family, the owners of Fox News, “probably” will be another investor, the president said last weekend in an interview on Fox News.

Congress had ordered the Chinese company ByteDance to divest itself of TikTok for national security reasons, in a law whose enforcement was delayed by Mr. Trump.

With its remarkable appeal to young people, TikTok is quite a prize. Oracle already has a relationship with the app, using its cloud servers to handle U.S. users’ data. But this new deal could give it access to the consumer-facing side of the business. Oracle’s biggest venture into a consumer business, the network computer in the 1990s, was a flop.

TikTok is just one part of the rapidly expanding Ellison family media portfolio. Mr. Ellison’s son, David, who recently secured an $8 billion deal for Paramount and CBS and is busy putting his own stamp on them, is widely reported to be preparing a much bigger bid for Warner, which includes CNN.

At any other time, the regulatory hurdles to owning TikTok, CBS and CNN along with a major swath of Hollywood would have been insurmountable. This is a decidedly different era, where being in the good graces of Mr. Trump counts for a great deal. The president said in January that he would like Elon Musk, then a close adviser, or Mr. Ellison to buy TikTok.

Powerful families have owned influential chunks of American media in the last century, but their reach was often limited by geography or other factors. The Chandler family, owners of The Los Angeles Times, held sway in Southern California for decades, but had little power elsewhere. Rupert Murdoch owns Fox and The Wall Street Journal, but their editorial missions do not entirely overlap.

In the digital era, the constraints are dissolving.

“Everything is consolidating,” said Michael Socolow, a media historian at the University of Maine. “What makes these deals different is that they are across multiple platforms. To have the opportunity to establish an editorial line across TikTok, CBS News and CNN — that’s a new world.”

Paramount declined to comment.

Money, a traditional restraint on media empires, is no obstacle to Mr. Ellison. On a recent day, he saw the value of his Oracle holdings increase by about $100 billion, making him briefly the richest man in the world. Mr. Ellison now has a net worth of $367 billion, according to the Bloomberg Billionaires Index. Mr. Musk is higher.

Mr. Ellison, 81, has been a presence in Silicon Valley much longer than any other founder. In 1977, he and two colleagues started Software Development Laboratories, which a few years later was renamed Oracle, after its principal database product.

He was less the technical genius than the chief salesman. Oracle had a few near-death experiences, but it survived and even prospered, unlike a vast majority of software companies from that era.

Along the way, Mr. Ellison was the prototype for the tech entrepreneur who worked hard and played hard. He has been married multiple times and owns large amounts of real estate, including the Hawaiian island of Lanai. He also owns a SIAI-Marchetti S.211 fighter plane, bought from the Italian Navy, and reportedly used it for mock dogfights with his son.

“Frequently, I’ll be in a meeting with someone and the person says, ‘Oh my god, you’re nothing like what I thought you’d be,’” Mr. Ellison said in a 2012 interview. “Of course, it’s a low bar. I didn’t just bite the head off a small animal before the meeting.”

Mr. Ellison had never previously shown much interest in the media beyond using many interviews in the 1990s to criticize the Microsoft co-founder Bill Gates, a longtime bête noire. His son is in discussions to acquire The Free Press, a new digital publication that presents itself in opposition to traditional news media. It is run by Bari Weiss, who is likely to be given some oversight of CBS. Ms. Weiss formerly worked as an editor for the opinion section of The New York Times and occasionally wrote essays.

Mr. Ellison, who didn’t return an email for comment, is accumulating money faster than he can develop plans to give it away. He has been consumed of late with a sprawling for-profit philanthropic entity he is building at the University of Oxford, on which he says he will be “concentrating my resources.” But in recent weeks, the research institute, called the Ellison Institute of Technology, has succumbed to some of the same upheavals that have befallen Mr. Ellison’s prior philanthropic exploits.

The billionaire has a long history of changing his mind on his charitable work, or splitting with the people he hires to oversee it. This month, Mr. Ellison parted with the person he had hired just last year to build E.I.T., John Bell, a well-known scientist who had given the project instant credibility.

Britain’s scientific culture is less commercial than the United States’, a situation that the institute aimed to change by developing numerous start-ups in the life sciences and other fields.

“We don’t have anybody like him in the U.K.,” Mr. Bell said about his benefactor. “And so to have him come here and say, ‘I’m going to build my legacy here in the U.K.,’ is an amazing step, actually. And he could have gone anywhere.”

In mid-August, Mr. Ellison brought on Santa Ono, the former president of the University of Michigan, with a title that seemed to outrank Mr. Bell. Mr. Ellison said Mr. Bell would “collaborate” with Mr. Ono. But two weeks later, Mr. Bell promptly announced his departure, calling the institute a “very challenging project.”

Mr. Ellison has been very hands-on at the institute, according to a person close to the entity, and had been regularly communicating with Mr. Bell and showing up for meetings at the institute’s Oxford offices. There has been tension within the institute’s leadership about how best to commercialize Mr. Ellison’s scientific research, along with persistent questions about how much the institute could trust Mr. Ellison’ to deliver on his financial commitments.