Jon Wagner joined Tesla in January 2013, and for almost five years (until September 2017) he was working on Model S, Model X, Model 3, and energy storage projects. Via LinkedIn:
"Jan 2013 – Team leader for battery pack design engineering: mechanical, thermal, structural, electrical, and system engineering. Led the cost-down and product improvement effort for Model S/X battery pack. Pushed R&D technology development focused on architectures for cost reduction, reliability, and safety. Brought many of those technologies to market in S/X, Powerwall, and Model 3.
Placed specific emphasis on employee and team development, leadership, and team culture. Overhauled performance reviews, compensation, recognition, and lightweight engineering process for rapid paced progress.
Also held Interim Director positions at various times for Body Engineering, Computer Aided Engineering, Materials, Battery Manufacturing Engineering."