J2 Global Inc. Chief Executive Vivek Shah has helped build an under-the-radar digital-media behemoth by buying up smaller companies. Now, he is getting a bigger war chest and a clear mandate to go on another shopping spree.

J2 Global—which owns a collection of assets including tech site Mashable, fax provider eFax and the videogame brand IGN—said earlier this year it is splitting into two companies. The bigger business, run by Mr. Shah, will get all of the media assets plus a $1 billion infusion to buy more. The spinoff business, called Consensus, will keep the slower-growing eFax.

In an interview, Mr. Shah said that the parent company will be renamed Ziff Davis, a nod to the century-old publisher. Mr. Shah said he picked the name—which calls to mind the heyday of the dot-com boom—because that publishing company survived an industry shake-up from print to digital and weathered a 2008 bankruptcy. Among Ziff Davis’s best known properties is PC Magazine, which chronicled the personal-computing revolution.

Mr. Shah, a former Time Inc. executive, led a private-equity buyout of the original Ziff Davis in 2010, purchasing the publisher for less than $25 million. He helped sell the company in 2012 to j2 Global for $167 million and was appointed CEO of the parent company in 2018. Earlier this year, Mr. Shah announced the spin off, which he said will simplify the business for investors. He owns less than 2% of the company.

“At its darkest moment, right after the great recession, we were able to recover,” Mr. Shah said. “Not many things live 100 years.”

The company—which will begin trading on the Nasdaq with the ticker symbol ZD in September—is making its market debut amid a far-reaching reordering of the media industry. Traditional TV, a cornerstone of the sector for more than half a century, is being supplanted by video-streaming. That shift has created a buying opportunity for players like Ziff Davis, as companies like ViacomCBS Inc. and AT&T Inc.’s WarnerMedia shed noncore assets to focus on streaming.

J2 spent $480 million on mergers and acquisitions in 2020, Mr. Shah said, and $2.5 billion on deals since 2013, buying companies including Mashable, online retailer Humble Bundle and coupon company RetailMeNot. The deal making has produced a $6.5 billion company with revenue of $1.49 billion in 2020, primarily from advertising and subscription businesses. Shares of the parent company, j2, closed Monday at $131.31, a roughly 86% increase over the past year.

“We see things that other people don’t see, look at the deals that aren’t being marketed,” Mr. Shah said. “And we exhibit a great deal of patience. We’ve passed on deals that have come back to us years later to transact on.”

The $1 billion that Ziff Davis will put toward deal-making includes $350 million in cash left on the balance sheet of the remaining company, about $400 million of debt capacity, plus an additional $250 million in borrowing capacity related to the disposal of its stake in Consensus, according to a person familiar with the matter.

Ziff Davis is relaunching into a digital-advertising market dominated by three tech giants, known in the industry as the “triopoly”: Alphabet Inc.’s Google, Amazon.com Inc. and Facebook Inc. Together, the companies increased their share of the U.S. digital ad market to a range approaching 90% in 2020 from 80% in 2019, The Wall Street Journal has reported.

But Mr. Shah said that he is bullish on advertising, which accounts for about 60% of the company’s revenue annually. Ziff Davis focuses on large advertisers in targeted sectors like pharmaceuticals, telecommunications and videogames, Mr. Shah said, and those categories have continued to deliver for the company even as the triopoly has increased its market share.

“While they are large dominant players, it’s still a fairly large market,” Mr. Shah said. “For the piece of the pie that’s available for the rest of us, we think we’re really well-positioned.”

Many of the digital-media businesses in Ziff Davis’s portfolio don’t rely on advertising. One of those is Speedtest, an iPhone app that allows users to test the strength of their wireless connections. Ziff Davis anonymizes the data from those speed tests, then sells it in bulk to telecommunications companies, which use it to determine the strength of their broadband networks, Mr. Shah said.

After the spinoff, Ziff Davis will hunt for deals that allow the company to target readers and advertisers in the consumer finance, travel and automotive categories, Mr. Shah said.

Mr. Shah said that Ziff Davis will continue to grow if it keeps generating a healthy share of advertising and subscription dollars from companies that are navigating the sometimes rocky transition to digital media from analog. Ziff Davis also hopes to grow by maintaining its focus on performance advertising, a form of marketing where clients pay for measurable online results.

“That playbook’s available to everyone, but not everyone has the ability to execute,” he said.

Write to Benjamin Mullin at Benjamin.Mullin@wsj.com

Corrections & Amplifications
Shares of j2 closed Monday at $131.31, a roughly 86% increase over the past year. An earlier version of this article incorrectly said the increase was 37%. (Corrected on Aug. 17)