In June, Jeremy Corbyn made a shock announcement: He would seek the leadership of Britain’s opposition Labour Party. In the months since, the little-known, left-wing member of Parliament has captured the imagination of a substantial bloc of voters who, a bit like American supporters of Bernie Sanders or Donald Trump, are disgruntled with politics as usual. The very real prospect of Corbyn winning the leadership vote on September 12 has filled many within the party establishment with dread because, they say, Corbyn is emblematic of the ideology that made Labour unelectable for years.

So what exactly is Corbyn’s worldview, and how might he govern if elected prime minister of the United Kingdom? Corbyn is a self-described “socialist” or “democratic socialist,” an old-school tax-and-spend left-winger who believes government spending—not austerity—is the key to economic stimulus. He wants to close the U.K.’s budget deficit by, in part, raising taxes on the rich and ending corporate subsidies.

Domestically, he wants to renationalize the country’s much-maligned railways, scrap university tuition, and introduce rent controls. Many of these positions enjoy widespread support, though another—his support of mass immigration to the United Kingdom—does not.

Corbyn has also raised fearswhich he has sought to tamp down—that he would reintroduce Clause IV of the Labour Party’s constitution. Here’s what the clause said:

To secure for the workers by hand or by brain the full fruits of their industry and the most equitable distribution thereof that may be possible upon the basis of the common ownership of the means of production, distribution, and exchange, and the best obtainable system of popular administration and control of each industry or service.

In other words, the party once committed to nationalizing industry. But Labour’s nearly two decades in the political wilderness in the 1980s and 90s prompted the party, under Tony Blair, to scuttle Clause IV. It was part of an effort to move Labour to the center of British politics—and it worked. Labour, under Blair, won the 1997 election and governed Britain until 2010.

Corbyn’s foreign-policy positions are unlikely to endear him to any occupant of the White House. He opposes British involvement in airstrikes against ISIS over Syria, wants to eliminate the country’s nuclear deterrent, and says he favors talks with his “friends” in Hamas and Hezbollah. And while he claims to favor the “harmonization of working conditions across Europe” through the European Union, he would oppose continued British membership in the bloc if it were based solely on the free market.

Corbyn, 66,  was voted into Parliament from Islington North in London in 1983, in an election that Margaret Thatcher’s Conservative Party won in a landslide, and he has left-wing politics in his blood. His parents met while campaigning for peace during the Spanish Civil War, and his political beliefs are so entrenched that he split with his wife of 12 years over the choice of school for their son. He says they remain on good terms, but that he felt “very strongly about comprehensive education,” or public schools.

The Financial Times has more:

During his 32 years as an MP, he has adopted a host of causes: antimonarchist, trade unionist, vegetarian, revolutionary. Known for his beige outfits and ascetic tendencies, he likes to cycle and has no car. He loves making jam with fruit grown on his allotment, belongs to the All Party Parliamentary Group for Cheese and is a train obsessive.

Although such attributes might normally turn a politician into a political punchline, these are not normal times for the Labour Party. The party was trounced by Prime Minister David Cameron’s Conservatives in the country’s general election in May, after which its leader, Ed Miliband—who himself had steered the party to the left—resigned. Enter Corbyn, whose candidacy and uncompromising positions have caught on in the face of opposition from his centrist rivals for Labour leader: Andy Burnham, Yvette Cooper, and Liz Kendall.

Most polls show Corbyn easily winning the Labour Party election. He has a large following among Labour’s party faithful, but those backing him also include Green Party members as well as some gleeful Conservatives hoping that his victory will sink Labour. Anyone who supports Labour’s aims can pay the equivalent of around $4.70 and vote in the leadership election. Needless to say, there has been a surge in people applying for membership.

Here’s a letter to the editor in The Telegraph newspaper that sums up what many people—supporters and critics—think about Corbyn:

Jeremy Corbyn is the only contender for the Labour leadership who clearly espouses the socialist ethos of workers’ rights and public ownership, the twin pillars of Labour principle. It is no surprise that Tory supporters are so vociferous in his condemnation.

It’s not just the Conservatives, or Tories, who are vociferous in their condemnation of Corbyn.

Cooper, Corbyn’s competitor for the leadership post, has accused Corbyn of offering “old solutions to old problems.” Former Prime Minister Gordon Brown, under whose leadership Labour lost the 2010 election, did not explicitly name Corbyn in remarks on the race delivered Sunday, but he did say:

I have to say that if our global alliances are going to be alliances with Hezbollah and Hamas and Hugo Chavez’s Venezuela and Vladimir Putin’s Russia, there is absolutely no chance of building a worldwide alliance that can deal with poverty and inequality and climate change and financial instability, and we’ve got to face up to that fact.   

No points for guessing who espouses those positions.

But perhaps the most biting criticism of Corbyn has come from Blair, now a much-reviled figure in Britain. Blair has argued that a victory for Corbyn could mean “annihilation” for Labour.

He also offered some advice: “People who say their heart is with Corbyn, get a transplant.”