Mr. Sweeney saw Apple as a central roadblock to that vision, according to people familiar with his thinking and documents unveiled in a recent court proceeding, because of the iPhone maker’s tight control over how people access “Fortnite” and any other mobile apps from Epic. Apple’s App Store takes a 30% cut of Epic’s revenue from those users.

Epic circumvented Apple’s fees and rules last August by introducing its own system for processing user purchases into mobile versions of “Fortnite.” It also prepared for a larger legal and public-relations campaign, complete with a video mocking a legendary Apple ad and the social-media hashtag #FreeFortnite.

“You’ll enjoy the upcoming fireworks show,” Mr. Sweeney said in an email to an ally at

Microsoft Corp.

on the eve of the plan’s launch. Apple made that email public in a court filing, along with other emails and witness testimony cited in this story.

Epic hoped to draw the company into a larger conflict, the court documents show. Once Apple and

Alphabet Inc.’s

Google booted “Fortnite” from their app stores, Epic responded by suing both companies.

The fate of Epic’s fight has widespread implications for the entire technology world. It could help determine everything from how much revenue app developers are able to keep to how exposed Apple could be to potential antitrust violations. Apple has rejected claims it has monopoly power, saying that Epic broke the terms of a contract and engaged in a smear campaign.

A resolution could be drawing near. Starting May 3, the dispute goes to trial before federal Judge

Yvonne Gonzalez Rogers

in Oakland, Calif. The judge must decide whether Apple is misusing its power to quash competition or if Epic is merely trying to break its contract with the iPhone maker to boost its bottom line.

Save the world

The man at the center of this clash is a 50-year-old programmer who prefers an office uniform of cargo pants and T-shirts. He eschewed the clubby confines of Silicon Valley to locate Epic’s headquarters just outside of Raleigh, N.C. Mr. Sweeney’s previous dealings with other technology companies showcase his instincts for big and prolonged fights, as well as an eye for strategy. The Maryland native is worth more than $9 billion, according to Bloomberg’s Billionaires Index.

He launched Epic from his parents’ basement at age 20 in 1991 and evolved his company from solely building games for PCs to include those for videogame consoles and smartphones. In 2012, he sold a 40% stake of his company to

Tencent Holdings Ltd.

, in part to tap the Chinese tech giant’s expertise in mobile gaming and wringing money from users through small purchases known as microtransactions. (Mr. Sweeney remains Epic’s largest shareholder.) Epic also owns the video-chat app Houseparty and makes the Unreal Engine, a suite of software tools for developing games and producing special effects for television shows, movies and other types of digital content.

Epic’s biggest hit started with the 2017 launch of “Fortnite: Save the World,” then a $40 game for up to four players to fight zombies and build forts. A few months later, after disappointing results, Epic offered up a new, free-to-play mode called “Battle Royale,” in which 100 players duke it out until only one combatant or squad remains. It later sold virtual currency that players could use to acquire in-game perks such as an outfit to make their avatars appear as a Marvel Comics superhero.

To build the community, since only a small percentage of players make such purchases, Epic pushed console makers to allow users of one machine to play “Fortnite” with users of another machine, in what would be an industry first for all three major videogame systems. That meant a PlayStation player could join a match with a friend on Microsoft’s Xbox or

Nintendo Co.

’s Switch.

Microsoft and Nintendo had shown a willingness for such cross-platform play.

Sony Group Corp.

balked.

In the fall of 2017, Epic updated its software that briefly allowed a Sony PlayStation “Fortnite” player to compete against someone on Microsoft’s Xbox. It pulled that function back, saying it was a mistake, after online chat boards lighted up with excitement. Seeing what was possible, gamers demanded more. Players cast Sony as the villain on social media with hashtags such as #blamesony and #notfortheplayers, a harbinger for the Apple dispute.

As Sony internally debated its position, executives were worried about exposure of its consumer-behavior data and competitors taking an unfair share of their business, according to people familiar with the talks. They felt Epic had backed them into a corner and worried that finicky gamers would turn on them, the people said.

Following months of negotiations, Sony relented. Asked about it afterward, Mr. Sweeney described it simply as “an effort in international diplomacy.” Since then, the Tokyo-based company has twice invested in Epic, having most recently contributed around $200 million in a funding round that valued Epic at $28.7 billion. A spokesman for Sony declined to comment.

Mr. Sweeney’s hardball tactics with Sony helped him usher in cross-play across videogame consoles, personal computers and Apple and Android devices.

All hands on deck

The relationship with Apple was cordial for its first decade. In March 2018, “Fortnite” was launched on Apple’s App Store. A year later, Mr. Sweeney was at the annual Game Developers Conference celebrating how cross-play had helped the game grow to almost 250 million players world-wide – a smashing success. Apple’s managers were happy to help promote the new hit, offering technical and marketing assistance to Epic.

Mike Schmid, head of Apple’s games business development for the App Store, helped oversee the “Fortnite” rollout and several updates. In a court statement, he described an “all-hands-on-deck treatment to address Epic’s non-stop asks, which frequently involved middle-of-the-night calls and texts demanding short-turnaround.”

To manage the work, he assigned someone in Australia so Apple could provide 24-hour coverage.

The relationship described by Apple in court papers differs greatly from the experiences detailed by other developers on Apple’s iOS mobile operating system. Smaller software makers have complained about what they perceive as Apple’s seemingly arbitrary rules and mercurial ways.

With Epic, Apple appeared to go out of its way to help the gamemaker establish itself on the platform. Mr. Schmid said Epic employees had told him Apple represented just 7% of its revenue. He couldn’t be reached for comment through Apple.

“On a variety of occasions, Epic personnel have told me that if Apple did not comply with its demands, Epic would simply terminate its relationship with Apple and remove its games off the iOS platform,” Mr. Schmid said in court records. A core part of Apple’s antitrust defense is that Epic’s games are available on a variety of tech companies’ platforms, not just Apple’s.

By early 2020, “Fortnite” was showing signs of aging, although popularity for online games can sometimes ebb and flow due to new seasons or features. The privately held company doesn’t disclose financial records but app-analytics firm Sensor Tower Inc. estimates global consumer spending within “Fortnite” on Apple devices had fallen in the first quarter of last year to $70 million from a peak of almost $180 million in the third quarter of 2018. Epic Chief Financial Officer Joe Babcock, who departed the company in early 2020, said it expected the trend to continue, according to a deposition he gave cited by Apple. Mr. Babcock couldn’t be reached for comment.

Epic disputes the notion that “Fortnite” was waning in popularity, as the company in May 2020 said it had reached 350 million registered accounts.

Epic hatched a plan, according to court records citing a board presentation, to revive interest in “Fortnite” beyond its seasonal updates and occasional music performances and movie screenings that people experience together in a virtual setting. Epic would turn to third-party developers to create new content for “Fortnite,” essentially turning it into an open platform unto itself.

But for this new plan to work, the company needed to find a way it could afford to compensate its would-be partners. Apple’s 30% share, the presentation concluded, was an “existential issue” for its plan and needed to be cut so Epic could share a majority of the profit with creators.

The battle begins

Last spring Epic began sharpening its plan to wrest itself from Apple’s fees and control. Its team investigated ways to surreptitiously add an alternative payment system to the versions of “Fortnite” on Apple and Google’s app stores, according to court records. By May Epic decided it would deploy the new system through a so-called hotfix, an important software update usually reserved for security bugs, records show, and do so just before the debut of the game’s new season.

Epic executives initially considered targeting Google alone, according to court records citing internal emails. But later they decided to include Apple, which in time would become the focus of the effort.

From an early stage, the plan depended on Epic’s payment system being rejected, read an email between Epic executives disclosed in court records. At that point: “The battle begins. It’s going to be fun!”

Epic co-founder

Mark Rein

predicted there was a greater than 50% chance Apple would immediately remove “Fortnite” from its platforms, according to an Epic employee deposition cited in court records. “They may also sue us to make an example.” Mr. Rein declined to comment.

While it worked on the technical attack, Epic also planned to cut prices on certain items in the console and PC versions of “Fortnite” by 20%— essentially creating a reason for players to eschew the mobile alternative offered by Apple.

But first, Epic would go to the front door and ask a favor of Apple and Google: The company wanted permission to run its own competing store and payment system.

In a late June email to Apple CEO

Tim Cook,

according to court records, Mr. Sweeney sought an exemption from App Store rules. Most important, he wanted to stop paying Apple’s 30% fee.

Apple rejected the request in a July 10 letter, laying out many of the same arguments it would make in defending itself against the eventual Epic lawsuit. Epic had other ways to sell its game, Apple’s lawyer added, as well as noting Epic collects royalties from games built on its software.

“Yet somehow, you believe Apple has no right to do the same, and want all the benefits Apple and the App Store provide without having to pay a penny,” the letter concluded. “Apple cannot bow to that unreasonable demand.”

Mr. Sweeney on July 17 responded with another email to Mr. Cook and others calling the response a “self-righteous and self-serving screed.” He promised to “continue to pursue this, as we have done in the past to address other injustices in our industry.”

Behind the scenes, Epic’s Project Liberty team met regularly and devised a way to present their plan to a judge and the public. The team included as many as 200 Epic staffers, outside lawyers and public-relations advisers. It developed an argument that Apple violated antitrust laws with its requirements that all apps offered on its iPhones and iPads go through its App Store and that all purchases of digital content go through the tech giant’s in-app purchase system.

It wasn’t a unique gripe. Other app makers, including

Netflix Inc.

and Spotify Technology SA, have also butted heads with Apple on its slice of fees and control. Apple says the walled mobile-software garden it built in 2008 is now responsible for more than a half-trillion dollars in commerce.

Epic’s team worried it wouldn’t be a sympathetic character in a public fight and that gamers would blame the company if Apple and Google ultimately decided to yank “Fortnite.” So it strategized on how to bring in additional companies, including smaller, sympathetic developers, to advocate for its cause, records say. It also studied past Apple responses to major public fights, focusing on its battle with the Federal Bureau of Investigation over demands to create a backdoor into the iPhone of a shooter in a 2015 terrorist attack in San Bernardino, Calif. The controversy subsided when the government found an alternative way into the device.

The Epic team concluded that Apple could be thin skinned when it came to its public image. “Nothing moves Apple to change other than notable consumer pressure,” an Epic memo noted.

As August approached, Epic’s board of directors was briefed on the project’s final pieces in a presentation dubbed “battle plan.” By this point, the board was told, Epic had spent time helping form the Coalition for App Fairness, an advocacy group, to support its crusade and it tested the payment system that would eventually be uploaded to Apple’s and Google’s app stores.

Mr. Sweeney sent emails to Sony, Microsoft and Nintendo alerting them to the upcoming price changes in “Fortnite,” a prelude to the “fireworks show.”

On Aug. 13, he lighted the fuse. “Epic will no longer adhere to Apple’s payment processing restrictions,” Mr. Sweeney wrote at about 2 a.m. in an email to Apple. Hours later, Epic flipped the switch on the new payment system and a public-relations campaign to rally gamers to its fight.

Project Liberty was in play.

Apple and Google both booted the game by day’s end, springing the second part of Epic’s plan: a legal battle.

A trial date hasn’t been set in Epic’s lawsuit against Google, though the situation is distinct. Devices that run Google’s Android operating system can download software from other app marketplaces in addition to the Google Play store. Google has said that Epic violated its app store’s policies as well, which are designed to keep it safe for users.

In the months after its lawsuit, Epic pursued complaints with regulators around the world and supported lobbying efforts among statehouses and Congress for changes that would crimp Apple’s power. It also released an online video that echoed Apple’s famous 1984 ad, a nod to George Orwell’s dystopian novel, that framed the computer maker as the underdog against the then-mighty

IBM.

This time around, the image of a televised Big Brother was replaced by one of a talking Apple wearing glasses similar to those of Mr. Cook. The call to action at the end read: “Join the fight to stop 2020 from becoming ‘1984.’ ”

Corrections & Amplifications
Joe Babcock is the former financial chief of Epic Games. An earlier version of this article misspelled his name as Mr. Babock. (Corrected on April 26)

Write to Tim Higgins at Tim.Higgins@WSJ.com and Sarah E. Needleman at sarah.needleman@wsj.com