That control is starting to fray as Mr. Johnson, a longevity guru known for performing experiments on his body, faces a backlash over the agreements.

SpaceX employees are working on plans for a Martian city, including dome habitats, spacesuits and researching whether humans can procreate off Earth. Mr. Musk has...

Ms. Shanahan, a lawyer who was married to Sergey Brin, a Google founder, led a rarefied and sometimes turbulent life in Silicon Valley, according to...