(Bloomberg) -- The veteran Apple Inc. executive who runs day-to-day operations at the App Store will be playing defense Thursday in the company’s trial with Epic Games Inc.

Matt Fischer will be the first Apple employee to take the witness stand as Epic, the creator of Fortnite, tries to convince a federal judge that the marketplace for apps that run on hundreds of millions of iPhones is operated like a monopoly. Trystan Kosmynka, a senior director at Apple in charge of the app review process, is set to be called to the stand later in the day.

Despite having a tenure with Apple of almost 20 years and being in charge of a business that’s estimated to generate more than $20 billion in revenue a year, Fischer keeps a low profile: He’s not featured on Apple’s website, he doesn’t appear at Apple product launch events and he rarely speaks publicly. He reports to Phil Schiller, the company’s top App Store executive, who is expected to be called as a witness later in the trial, along with Chief Executive Tim Cook.

Topics Fischer may be questioned about by Epic’s lawyers include App Store business strategy, finances, policies and practices, and market power over iOS devices, according to court filings. Kosmynka, who reports to Apple’s developer relations chief, will be asked about the app review process and App Store curation.

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The trial in Oakland, California, comes as Apple faces a backlash -- with billions of dollars in revenue on the line -- from global regulators and some app developers who say its standard App Store fee of 30% and others policies are unjust and self-serving.

The fight with Epic blew up in August when the game maker told customers it would replace Apple’s in-app purchase system with its own, circumventing Apple’s commissions from add-ons inside of Fortnite. Apple then removed the game, cutting off access for more than a billion customers.

Apple, which vehemently denies abusing its market power, has called Epic’s legal gambit a “fundamental assault” on a business model that is beneficial to both developers and consumers.

In the first three days of the trial, Epic put on testimony by its CEO, Tim Sweeney, and other executives at the game maker to make the case that the App Store is a like a “walled garden” that has left users and developers “trapped” in an anticompetitive marketplace.

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Epic has also called as witnesses executives from other companies with gaming businesses, including Microsoft Corp. and Nvidia Corp., to show that they, too, have been constrained by onerous App Store rules.

Apple has its used its cross-examination of witnesses to try to undercut their credibility and poke holes in Epic’s antitrust claims.

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