The billionaire SoftBank founder promises to invest $100 billion in the US as part of a sweeping redemption plan.

When Masayoshi Son made a surprise appearance at Mar-a-Lago alongside Donald Trump last week, the founder of Japan's SoftBank Group Corp. vowed to invest a stunning $100 billion in the US over the next four years. The president-elect joked that perhaps SoftBank would like to double that target to $200 billion. Not to be outdone, Son replied with a wide smile, "I will really try."

That may not be an exaggeration. The Japanese entrepreneur is quietly plotting one of his trademark bet-the-company moves that's likely to cost as much as his initial pledge -- and perhaps a good bit more. Over the past few months, according to people directly involved, Son has developed a singular obsession: how to build the next Nvidia Corp. with his own chip and rake in some of the tens of billions of dollars being spent on artificial intelligence hardware.