Getty Images Epic Games, the private company behind the massively popular video game Fortnite, will take on the world's most valuable company in court Monday. In Epic Games v. Apple, Silicon Valley's highest-stakes court case in a decade, the Cary, North Carolina-based game maker will argue that Apple unfairly uses it dominance to lock developers into using its App Store, which it says takes too hefty a slice of their profits. Epic will attempt to make the case that the App Store represents an illegal use of Apple's market power. Even if Apple is a legal monopoly, according to the antitrust complaint Epic filed in August, the company is using its power to dominate a secondary market: app distribution. Third-party developers are dependent on the App Store for customer transactions on more than one billion iPhones, and Apple charges them up to 30 percent of every purchase, which Epic's complaint says is 10 times what other systems, such as Nintendo or Xbox, charge on average. Epic argues that "the anti-competitive consequences of Apple's conduct are pervasive."