SoftBank is the "Nasdaq whale" that has bought billions of dollars in U.S. stock derivatives in a move that fueled the feverish rise of big technology companies before a sharp setback on Thursday.
Regulatory filings demonstrated that SoftBank purchased near $4 billion in shares of large tech stocks, including Tesla. They had bought a roughly equal amount of call options tied to the underlying shares it bought, according to people familiar with the matter. It also sold call options at far higher prices. This allows SoftBank to profit from a near-term run-up in stocks and then reap those profits by unloading its position to willing counterparties.
To read more about how they are influencing the market, take a look at this article from the Wallstreet Journal.