He promises socialist reforms vowing to take his party’s leadership further to the left than it’s been in decades. Huge crowds are turning out to hear his message. We’re not talking about Vermont Senator Bernie Sanders — this is Jeremy Corbyn, the man in line to become the next leader of Britain’s Labour Party.

The 66-year-old has been a member of parliament since 1983, representing Islington North, a borough of London.

“The meetings that he’s more used to are things like church halls or community centers with 30, 40, or 50 people turning out. I went to one of his rallies last week, 1,500 peopled turned up,” says the BBC’s Mobeen Azhar, who has been tracking the Corbyn phenomenon. “It had the atmosphere of a concert or an album launch, more than a political rally. He really is a rock star at the moment.”

Corbyn has been advocating a shift away from austerity measures in Britain, away from the current focus on reducing the deficit and public spending. Corbyn proposes policies like quantitative easing, printing more money that can be pumped into the welfare state. Corbyn has also advocated for public ownership of large infrastructure such as Britain’s rail service.

“What he’s known for is being rebellious,” says Azhar. “He has voted and ignored the party whip over 500 times. He’s also known for doing things like speaking out against the war on terror.”

He also doesn’t own a car and holds the record for the lowest expense claimed in Parliament.

Former prime minister and head of the Labour Party, Tony Blair, is less-than-thrilled with Corbyn’s remarkable and unexpected ascent and his attempt to shift the party back to its socialist roots. Blair, who steered the party more toward the center, said the threat from Corbyn would make the party unelectable. He said that if people believe they’re voting with their heart, “get a transplant.”

Other Labour leaders have told their supporters to back anybody other than Corbyn.

They don’t seem to be listening. Recent polls suggest that if a vote were held today, Corbyn would become Labour’s new leader. The result of the contest will be announced on September 12th.

But could a victory carry him to the top spot in Britain, the prime minister’s residence at 10 Downing Street in London?

“That’s another question. It seems unlikely. But what you’ve got to remember is that even a few weeks ago, it seemed very unlikely that we would be talking about Jeremy Corbyn as the next Labour leader,” says Azhar. “Things are changing and they’re changing very fast.”