Amazon is the most sought-after employer in the US. We went inside to find out why

The first three times Amazon tried to hire him, Gerard Medioni said no. As a tenured professor at the University of Southern California, known around the world for his computer-vision expertise, he was well settled in his dream job. In early 2014, he agreed to give a guest lecture at Amazon's Seattle headquarters, but nothing more. Setting boundaries one more time, Medioni initially refused to write a job-applicant essay that an overeager Amazon executive requested.

"I'm a professor," Medioni reminded everyone. "I give homework; I don't write homework."

Then everything changed when Amazon told Medioni about a secret project: building a grocery store that wouldn't need checkout lines, because computer vision could flawlessly track shoppers' actions. Stunned by Amazon's audacity, Medioni shot back: "Do you have any idea how hard this is?" Amazon's response: "Yeah, we know." Unfazed, Amazon was ready to spend many millions of dollars to make this futuristic vision of retailing come true.