Tesla was incorporated in 2003 after years of engineering research and experimentation. Musk first got involved in 2004 by becoming the largest shareholder. He became CEO in 2008 and in 2009 he settled a lawsuit that allowed him to be legally called a "cofounder" of the company and has liberally used the title ever since
From what I remember of the early blog posts on the site, his side of the story is that when he invested in it, the only thing the company had was an electric motor design, and that the funding round was in an effort to turn the motor into an EV instead of selling off the surrounding IP and patents.
Even if you don't take his word, it's tough to suggest that he isn't effectively responsible for all of Tesla's success, at least in terms of knowing when the technology was ready to be turned into serious cars and hiring the right people to achieve that, both in terms of design and getting the production lines to scale (which was the prerequisite for the 2018 stock bonus that is now responsible for a large portion of his stake in TSLA/net worth).
Eh, idk I guess I'd like to see some sources for that. Even the Wikipedia's entry on the Roadster calls out that:
> Elon Musk took an active role within the company and oversaw Roadster product design at a detailed level, but was not deeply involved in day-to-day business operations
He was certainly the primary person keeping them afloat financially. By January of 2009 the company had raised $187 million and $70 million of that was Musk. That was just before Tesla finally caught it's big break in June of that same year when it got $465 million from the US DoE, by far its biggest investment
But even on the financial side of things he's caused many headaches for the company. Like in 2016 when he made Tesla buy his cousins' (failing) solar company, SolarCity. Of course he neglected to mention to Tesla shareholders that it was failing