Apple Watch Saga Set in Motion by Late-Night Email to Cook (2)

At about 1 a.m. California time in 2013, a scientist emailed Apple Inc. Chief Executive Officer Tim Cook with an irresistible pitch.

“I strongly believe that we can develop the new wave of technology that will make Apple the No. 1 brand in the medical, fitness and wellness market,” he wrote in the email, which was later included in legal documents. Some 10 hours after the message was sent, an Apple recruiter was in touch. And just weeks after that, the engineer was working at the tech company on a smartwatch with health sensors.

A flurry of activity began. Within a few months ...