At the start of a call Wednesday to provide guidance on Tesla’s record sales but $408 million loss in the second quarter, Tesla CEO Elon Musk dropped a bombshell: that its chief technical officer, JB Straubel, will be stepping down from his executive post. 

Drew Baglino will take over most of the responsibilities held by Straubel, who will be transitioning to the role of senior advisor. 

The departure of Straubel is a huge loss for the company. He’s considered a co-founder of Tesla, as well as an expert on energy storage and propulsion—and in many intents and purposes was Musk’s partner in Tesla’s rise.

The Stanford grad has been the mastermind behind key decisions made on Tesla’s power systems and battery technology—decisions that have given the company a continued advantage in efficiency and driving range after other companies have created rival electric models. To this day he's considered one of the world's top experts in vehicle battery tech.

Straubel's public role for the company has often played well with Musk’s zeal. He was composed and engaging, often chiming in on company calls or presentations with smart answers to technical points; he provided some deep-dive insight on the company’s tech in blog posts that made a real difference early on for fans and followers; and he was approachable, helping provide rides and demos at product events. In a 2016 speech, prior to the launch event for the Model 3 and the hundreds of thousands of advance orders to follow, Straubel said, “I never imagined that things would scale or grow as quickly as they have.”

Tesla Model 3 design prototype - reveal event - March 2016

Tesla Model 3 design prototype - reveal event - March 2016

But Tesla and its share price did grow quickly, and it earned him tremendous wealth. According to Bloomberg, Straubel has offloaded Tesla shares eight times in the past nine months, in transactions netting him about $30.1 million. 

After Musk announced the change Wednesday, Straubel chimed in and said, “Yeah, it’s been a great adventure, 16 years.”

Straubel, who was in his 20s when the company started work on its Lotus-based Tesla Roadster, added some reassuring words: “I’m not disappearing, and I just wanted to make sure that people understand that this was not some, you know, lack of confidence in the company or the team or anything like that.”

Musk reminisced briefly about the first meeting he had with Straubel, at McCormick & Schmick's in El Segundo. “If we hadn't had lunch in 2003, Tesla wouldn't exist, basically.” 

The initial premise of that meeting, Straubel has previously said, was to get Musk to financially support Straubel’s electric airplane project. Electric cars were looking like a long shot for a startup in 2003; perhaps electric airplanes may take off in the next decade, with Straubel the pilot.