After 15 years at the helm, Tim Cook is stepping down as CEO of Apple and handing over the reins to the company’s senior vice president of hardware engineering, John Ternus . Cook, who joined Apple in 1998, succeeded Steve Jobs in 2011 and went on to transform Apple into a powerhouse worth $4 trillion.  With his time as CEO coming to an end on September 1, let’s take a look at some of the highlights of Cook’s 15 years as the leader of one of the most influential companies in the world.