When Musk 'joined' Tesla it was a name and two other guys. The latter two of whom left the company before a single car had been produced. They then sued for the right to be called founders a couple of years after they left, and once it became clear the company would stand a reasonable chance of success.
If my memory serves me correctly, they had put some Sony Handicam batteries on a chasis and driven it around before Musk. Musk was there for every actual product and its development.