Thats right in Paypal and Tesla's cases, he bought them and then gave himself the title of founder, but he did actually found SpaceX. Per wiki:

In early 2001, Elon Musk met Robert Zubrin and donated US$100,000 to his Mars Society, joining its board of directors for a short time.[11]: 30–31  He gave a plenary talk at their fourth convention where he announced Mars Oasis, a project to land a greenhouse and grow plants on Mars.[12][13] Musk initially attempted to acquire a Dnepr intercontinental ballistic missile for the project through Russian contacts from Jim Cantrell.[14]

Musk then returned with his team a second time to Moscow this time bringing Michael Griffin as well, but found the Russians increasingly unreceptive.[15][16] On the flight home Musk announced he could start a company to build the affordable rockets they needed instead.[16] By applying vertical integration,[15] using inexpensive commercial off-the-shelf components when possible,[16] and adopting the modular approach of modern software engineering, Musk believed SpaceX could significantly cut launch cost.[16]

In early 2002, Elon Musk started to look for staff for his company, soon to be named SpaceX. Musk approached five people for the initial positions at the fledgling company, including Michael Griffin, who declined the position of Chief Engineer,[17] Jim Cantrell and John Garvey (Cantrell and Garvey would later found the company Vector Launch), rocket engineer Tom Mueller, and Chris Thompson.[18][19] SpaceX was first headquartered in a warehouse in El Segundo, California. Early SpaceX employees, such as Tom Mueller (CTO), Gwynne Shotwell (COO), and Chris Thompson (VP of Operations), came from neighboring TRW and Boeing corporations. By November 2005, the company had 160 employees.[20] Musk personally interviewed and approved all of SpaceX's early employees.[21]