Tom Steyer, who made his first appearance in the Democratic debates on Tuesday night, is a hedge fund billionaire who has funded efforts to impeach President Trump and regularly decries “the corporate stranglehold on democracy.”

The 62-year-old, who lives in San Francisco, started the hedge fund Farallon Capital in the 1980s and has funded the groups Need to Impeach and NextGen America. He sold his ownership stake in the hedge fund, which had major investments in coal, in 2012.

He has portrayed himself as a progressive outsider, calling for measures like decriminalizing illegal border crossings and expanding the Supreme Court. He has also emphasized climate change on the campaign trail. He has no prior experience in elected office.

Mr. Steyer, a major Democratic donor, has been dismissive of party leaders’ reservations about impeachment. He has directed tens of millions of dollars into television commercials in which he argued that the president was a threat to the country. (The president responded on Twitter to one ad, calling Mr. Steyer a “weirdo.”)