Elon Musk has taken a major stake in Twitter, regulatory filings showed Monday, sending the social media network’s stock soaring and igniting speculation he could seek an active role in its operations.

Musk, the world’s richest man and CEO of electric vehicle company Tesla, is a frequent Twitter user, who often posts controversial messages and announcements and has long been critical of social media companies.

In one recent post, he questioned Twitter’s adherence to free speech and hinted at launching his own platform.

According to a document filed with the US Securities and Exchange Commission (SEC), the South African-born billionaire acquired nearly 73.5 million Twitter shares — a 9.2 percent stake in the company.

Based on Friday’s closing price of the company’s stock, his investment amounts to nearly $2.9 billion.

Investors responded quickly. At 7.15 am in New York (1115 GMT) Twitter’s stock was trading at about $49, up by around 26 percent.

“We would expect this passive stake as just the start of broader conversations with the Twitter board/management that could ultimately lead to an active stake and a potential more aggressive ownership role of Twitter”, analysts Daniel Ives and John Katsingris of Wedbush wrote in a note.

Musk launched a poll on Twitter on March 25, saying “free speech is essential to a functioning democracy. Do you believe Twitter rigorously adheres to this principle?”

More than two million people voted in the poll, with over 70 percent saying “no.”

“Given that Twitter serves as the de facto public town square, failing to adhere to free speech principles fundamentally undermines democracy. What should be done?” he continued the next day.

“Just buy Twitter”, was one of the first responses from tens of thousands of users.