Before March 2021, Elon Musk’s charitable foundation had never announced any donations to Cameron County, an impoverished region at the southern tip of Texas that is home to his SpaceX launch site and local officials who help regulate it.

Then, at 8:05 one morning that month, a SpaceX rocket blew up, showering the area with a rain of twisted metal.

The Musk Foundation began giving at 9:27 a.m. local time.

“Am donating $20M to Cameron County schools & $10M to City of Brownsville for downtown revitalization,” Mr. Musk said on Twitter.

Mr. Musk, the world’s second-richest person according to Forbes, presides over SpaceX, Tesla and other companies that are pushing the boundaries of technology, while also controlling a social media platform, now known as X, through which he promotes his often-polarizing political and social views.

At the same time, he runs a charity with billions of dollars, the kind of resources that could make a global impact. But unlike Bill Gates, who has deployed his fortune in an effort to improve health care across Africa, or Walmart’s Walton family, which has spurred change in the American education system, Mr. Musk’s philanthropy has been haphazard and largely self-serving — making him eligible for enormous tax breaks and helping his businesses.