My understanding (IANAL) is that "Tesla" is trademarked by the company. [1] Note that doesn't mean no one else can ever use that name for anything. It does mean I'd probably get a cease and desist letter if I tried to go into the car business under the name Tesla. But I can probably get a trademark in other areas where there isn't a serious possibility of confusion. How close I'm willing to get to that line probably depends on how badly I want the name and how conservative the lawyers are.

[1] https://www.lexology.com/library/detail.aspx?g=e4eaa83d-47dc...