It helps when NASA is laying off everyone you need to hire, and they have no other choice of a place to work (unless they like blowing up poor kids in poor countries for Raytheon).
It should also be noted that he was not a founder at Tesla, even. He bought his way in.
>It helps when NASA is laying off everyone you need to hire, and they have no other choice of a place to work
Actually Musk has said in the past that they had a LOT of trouble hiring early on. They had goals of reusable rockets right around the start of the company, and most people in the industry didn't take them seriously.
Nobody wanted to work for the laughing stock of a company that dreamed of doing something that most thought was impossible (affordably reusing rocket stages).
He founded Tesla through force of will. They had a concept but no funding and no drivetrain. Elon got them funded and hooked them up with an engineer he had been funding to build a drivetrain. Their original roadster was going to cost $200,000+ just to build, Elon pushed them out of the way and saved the company.
If he hasn’t gotten involved, it would have failed. That’s indisputable. The common usage of founder nowadays doesn’t require someone was an employee on day 1, it means they were instrumental in its early days and Elon certainly was.
It should also be noted that he was not a founder at Tesla, even. He bought his way in.