Billionaire Tom Steyer has announced a 2020 presidential campaign, adding his name to a crowded pool of Democrats vying to unseat President Donald Trump.
An environmentalist and advocate for the movement to impeach Mr Trump, he has donated millions to liberal causes.
Mr Steyer’s launch video focused on “pushing power down to the people” and blaming corporations for most of the nation’s “intractable” problems.
The California financier had previously said he would not run for office.
Forbes lists Mr Steyer’s net worth at $1.6bn (£1.2bn).
“Americans are deeply disappointed and hurt by the way they’re treated by what they think is the power elite in Washington DC,” Mr Steyer, 62, said in his campaign video.
“Almost every single major intractable problem, at the back of it you see a big money interest for whom stopping progress, stopping justice, is really important to their bottom line.”
He used climate change and the opioid crisis as examples of how corporate interests were negatively affecting the nation.
Mr Steyer also highlighted his own philanthropy, saying he had pledged to give away half of his wealth during his lifetime and had supported causes like young voter engagement and clean energy.
He heads the group Need to Impeach, which supports removing Mr Trump from office, and has spent millions backing Democratic candidates during previous election cycles.
According to the Center for Responsive Politics, Mr Steyer and his wife, Kathryn, are the second biggest political donors in the US, just behind Republican donors Sheldon and Miriam Adelson.
Mr Steyer has teased running for office before.
US media have described Mr Steyer’s campaign as the Democratic version of Mr Trump’s; both men are political outsiders with vast personal wealth, running on the premise of changing the existing system.
Mr Trump has called Mr Steyer “wacky”, “totally unhinged” and a “weirdo”. He has not commented since Mr Steyer’s campaign launch.
A spokesman for Mr Steyer told the New York Times Mr Steyer had pledged to spend at least $100m on his presidential campaign – which exceeds early fundraising totals for Joe Biden ($21.5m), Elizabeth Warren ($19m), Pete Buttigieg ($24.8m), Bernie Sanders ($18m) and Kamala Harris ($12m).
But in order to qualify for the next set of Democratic debates on 30 and 31 July, Mr Steyer will need to meet donor or voting thresholds set by the Democratic National Committee.
His campaign must reach 1% in the polls or obtain donations from 65,000 donors, of which 200 must be from 20 different states.
If he does not qualify by then, he will have to wait until the next round in September.
Mr Steyer’s entrance comes as fellow Californian Congressman Eric Swalwell became the first 2020 hopeful to drop out of the race.
On Monday, Mr Swalwell said he had no regrets, but, “we have to be honest about our own candidacy and viability”.
He will instead be seeking re-election to the House of Representatives.
But the pool remains crowded, with two dozen candidates.
Joe Sestak, a former Pennsylvania congressman and three-star vice admiral in the US Navy, is another late start contender.
He announced his campaign at the end of last month, focusing on climate change and global policy.
Who will take on Trump in 2020?
Tom Steyer has joined the race to stop Donald Trump from being re-elected. But who else has a shot at becoming the next president?