The new iPhone 15 is about to hit the stores, and Apple CEO Tim Cook might have already sent one to his most important investor — Warren Buffett. He bought Apple shares after realizing how devoted people are to its phones, and its unique ability to keep consumers spending within the Apple ecosystem. His return has been well over $100 billion on paper, making Apple Buffett's best investment over the past decade. "Our railroad is a very good business, but it's not remotely as good as Apple's business," Buffett said at the Berkshire shareholder meeting in May . The billionaire investor has called Apple Berkshire's "third-largest business," after its insurance and railroad holdings.

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Persons: Tim Cook, — Warren Buffett, Buffett, Ted Weschler, Todd Combs, Ben Graham, Cook, buybacks Buffett, repurchases, Apple's Organizations: Apple, Oracle, New, Wall, CNBC Locations: Berkshire, Omaha