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They call him Tim Cook’s Tim Cook. Apple’s operations chief Jeff Williams may be less well known than some of the technology giant’s other senior executives, but when he stepped on the stage at the Code Conference he demonstrated a relaxed mastery of a range of topics, from the intricacies of Apple’s complex supply chain to the long-range potential of ResearchKit.

As one of Cook’s trusted lieutenants, Williams has played a significant role in Apple’s entry into new categories, including the recent debut of the company’s first smartwatch, and, before that, the mobile phone market with the launch of the iPhone. He has overseen worldwide operations for the iPhone since 2007.

Williams oversees a sprawling logistics operation that, at its peak, employs some 40,000 people to support the iPhone. Over the recent holiday quarter, Apple shipped 74 million iPhones — so many that, if stacked like pancakes, the slender mobile devices would reach the International Space Station, he notes.

“They were built, produced and shipped in 90 days,” Williams said.

Williams chafed at questions about labor conditions at factories in China, saying Apple has a team devoted to ensuring that the people who manufacture the company’s products are treated fairly. When pressed about the spate of suicides at one Foxconn facility in 2010, he and Cook personally investigated.

“We learned it had nothing to do with working conditions,” Williams said, echoing an observation Apple co-founder once made about the suicide rate at Foxconn. “[The factory had a] lower suicide rate at their biggest cluster than any place in the US. By that standard, it’s the happiest place on earth.”

Williams resisted pressure to quantify early sales of the Apple Watch, generically describing demand as “fantastic.”

“Obviously, I can’t give you that number,” Williams said Wednesday at the Code Conference, after Walt Mossberg pressed him to put some numbers next to his adjectives.

Williams confirmed that Apple will release a developer kit that will allow companies to write apps directly for the Apple Watch next week, at the start of the Worldwide Developers Conference on June 8.

“I’m a cyclist who uses Strava, so it will have access to the sensor,” Williams said.

Williams seemed to hint at Apple’s interest in the automotive market in his response to one question about what the company plans to dow with its huge cash hoard.

“The car is the ultimate mobile device,” Williams said, quickly adding. “We’re exploring a lot of different markets.”

Williams said that the deciding factor in choosing new businesses is not the opportunity for revenue growth, but rather “which ones are ones [in which] we think we can make a huge amount of difference.”

One area with growing potential is ResearchKit, software that allows Apple’s iPhone to be used as a tool for medical research. Williams said the technology already is being used to aid the study of Parkinson’s Disease, heart health, breast cancer and asthma.

“Usually it takes a year-plus to see results, we’re seeing (it) in weeks and months,” Williams said.