In 2013, Landon Mossburg, then 29, was hired by Tesla to work on its supply chain team. Tesla threw him into negotiations with the senior executives of cellphone, internet and tech companies to secure internet connectivity deals that would feed Tesla’s over-the-air software updates. Mossburg had a bachelor’s degree in business and had worked as a consultant for Accenture and KPMG. But business wasn’t really a passion for him—writing code was. So on nights and weekends, Mossburg began writing code to resolve issues he noticed in Tesla’s Fremont, Calif., factory: Among his first projects was a simple program that helped the early Autopilot team label stop signs and stop lights in images of intersections.