Think of Cook’s job as a $900 billion balancing act. After nearly seven years as CEO, he has proved to be far more than a transitional figurehead after Steve Jobs. Cook has maintained Apple as a cash-­generating machine without sacrificing innovation. He engages ­gingerly with China’s rights-challenged government, even as he leads ­Apple’s pro-privacy ­crusade. Should Apple ever be worth $1 trillion, his place in the leadership pantheon will be forever secure.