Epic Games CEO Tim Sweeney — the guy behind Fortnite — has been fighting Apple and Tim Cook over its App Store rules for five years. I asked him why.

Apple was forced to change its App Store policies to allow developers to link users to external websites for payments. This was a major shift, and just last week, a judge ruled that Apple hadn’t followed the court’s order properly and held the company in contempt of court.

Apple on Monday lodged an appeal to challenge a U.S. judge’s ruling that ordered the tech company to immediately open its lucrative App Store to more competition.