SoftBank was founded by Masayoshi Son. It was originally a tech company that resold software (imagine Steam but for desktop apps), but very quickly it morphed into something like a PE firm that would do continual leveraged buyouts of existing firms. They've bought companies that run conferences, tech magazines, one of their more formative M & A deals was to buy the Japanese Vodafone arm. Many of these deals actually went pretty poorly, with Masayoshi overpaying for the firms he bought and then being saddled with very large debts to repay the loans. Masa was wiped out and faced bankruptcy multiple times.

Later on the would move away from leveraged buyouts and start investing in startups more similar to how a VC firm would in the US. He notably invested early in Yahoo and Alibaba.