$3bn shares

Elon Musk just became Twitter's largest shareholder

The ultimate aim of Musk's 73.5 million share purchase worth $2.9 billion, based on the closing price Friday, is not clear. Yet in recent weeks Musk, who has 80 million Twitter followers and posts there often, has questioned free speech on Twitter and whether the platform is undermining democracy.

The regulatory filing Monday describes Musk as a long-term investor looking to minimize his buying and selling of the shares.