This is a straightforward CEO succession announcement: Tim Cook is stepping down after 15 years leading Apple, with John Ternus (SVP of hardware engineering) taking over. The article backs the $4 trillion headline by comparing Apple's market cap growth from $350 billion (2011, when Cook became CEO) to over $4 trillion today—a 1,000% increase. It also cites revenue quadrupling ($108B to $416B) and iPhone revenue jumping from $47.1B to $209.6B over the same period. Cook will remain as executive chair. Ternus faces immediate challenges: catching up on AI (Siri reportedly getting Google's Gemini), launching a foldable iPhone, smart glasses, and AI-focused hardware. The source doesn't explain *why* Cook is stepping down now—it just states he is, which is notable for a retirement announcement. Stock performance (2,000% gain vs. S&P 500's 500%) is cited as supporting evidence of Cook's tenure value.