When Cook took over Apple, the iPhone had already pointed the way forward. Fifteen years later, as Cook concludes his 15-year tenure as Apple's CEO, stepping down on August 31 (local time in the U.S.) and to be succeeded by John Ternus starting September 1, the tech giant, with a market capitalization of $4.67 trillion, is facing new challenges: there is still no clear path for its next growth trajectory. Cook will not completely step away after his resignation; he will transition to the role of executive chairman of the board, continuing to participate in certain company affairs.