After 15 years, Tim Cook is stepping down as Apple’s top executive. At age 65, he leaves behind a hardware juggernaut that, under his leadership, brought about a global smartphone revolution and transformed Apple into one of the most profitable publicly traded companies in history. With a reputation for logistical management, Cook first joined Apple in 1998, overseeing its worldwide sales and operations. In 2009, he temporarily began running day-to-day operations when the company’s legendary co-founder, Steve Jobs, took medical leave due to complications from pancreatic cancer. In 2011, just a few months before Jobs’s death , Cook took over as CEO. Filling Jobs’s shoes was seen as a tremendous task, but company observers say that despite a more subdued demeanor , especially on stage, Cook met the challenge. “Steve Jobs was never going to be an easy act to follow,” said Dipanjan Chatterjee, a principal analyst for market research firm Forrester.…