Nino Governale was the perfect target for the teenage Matteo Salvini. The PE teacher hailed from Sicily and could hardly get through the weekly lesson at the prestigious Alessandro Manzoni high school in Milan without being goaded by his pupil.

“Salvini was as arrogant at 14 as he is today,” Governale says. “His favourite game was to antagonise. At that time he was against all southerners – we were the enemies coming to Milan and stealing jobs.”

Governale, who is now retired, switches over the channel at his Milan home whenever he sees the Italian deputy prime minister and leader of the far-right League appear on TV, even more so now as Salvini campaigns for the European parliamentary elections.

It is a campaign that has taken him both across Italy and beyond. In Budapest, Hungary’s nationalist prime minister, Viktor Orbán, welcomed Salvini as “the most important person in Europe today.” On Saturday, he is attempting to burnish his credentials as the leader of Europe’s far-right with a rally on his home turf, at Milan’s magnificent Piazza Duomo, with Marine Le Pen among the other speakers. A Facebook campaign is calling on protesters to converge on the city.

Matteo Salvini, left, in Hungary with the country’s nationalist prime minister, Viktor Orbán. Photograph: Szilárd Koszticsák/EPA

In less than a year, Salvini has gone from taking the League to third place in the 2018 election to eclipsing its coalition partner, the Five Star Movement, as Italy’s biggest party. Final polls on voting intentions in the EU elections gave it around 30%, up from the 6.4% it gained in the 2014 European vote.

It is a political story that began in Milan: the northern Italian city regularly returns leftwing candidates, but in the late 1980s, a new political force, the Lega Nord – or Northern League – was gathering strength. The party made the separation of Italy’s wealthy north from the poorer south its rallying cry. Salvini joined in 1990, when he was still at school, and went on to lead the youth wing, regularly canvassing in squares and markets across the city.

“His behaviour was already perfectly political,” Governale says. “The thing that astonishes me today is that so many people from the south, who Salvini said such awful things about, support him.”

Mariella Messa Parravicini, a former Latin and Greek teacher at Manzoni school, also detected the early makings of a politician. “I wouldn’t say he was kind … but he was an intelligent student, and also very interested in shaping the classes with his own theories,” she recalls.

The creation of a succession of enemies – southerners, immigrants, the EU, Roma people, Muslims and, more recently, leftwing “do-gooders”, particularly those who help migrants – formed a reliable component of his political ascent.

Lampooning his foes has been a staple element of his recent rallies. “Where are the communists?” he asked at a recent rally in Ascoli Piceno, a town in the central Italian region of Marche, a stronghold of the left since the end of the second world war. “Because usually about 10 of you turn up,” he mocked.

Communist ideals however helped shape his early populism. In 1994, a year after being elected a councillor in Milan, Salvini supported protests against the Northern League mayor over a crackdown on a social club known as a hub for radical leftwing debate that he had frequented in his teens. He once told a newspaper that he relates to “classical themes of the left”.

Those sympathies were discarded as Salvini rose through the party ranks, eventually becoming leader in 2013 and tilting it further towards the far-right as he capitalised on the fallout of the financial crisis and a surge in migrants arriving by sea.

He also broadened the party’s appeal by taking it national (the word “northern” was dropped from its name) and repositioning it as a “defender of European rights”.

He knows what affects the common man, he dresses, speaks and behaves like the common man Stefania Piazzo

Stefania Piazzo, a former director of La Padania, the party’s now shuttered newspaper, described Salvini as the Zelig – the ultimate chameleon who pops up everywhere in different guises – of Italian politics. He used to work at the paper one day a week in the mid-1990s, putting together the letters’ page.

“He is capable of quickly adapting – for example with the euro, when he realised it wasn’t perceived by people and businesses as the absolute evil, he let it drop,” she says.

“He knows what affects the common man, he dresses, speaks and behaves like the common man. He also had a huge stroke of luck in finding the right conditions – there is no longer a moderate party or strong representative of the left.”

She compared Salvini’s character to an ECG chart – “always hyper, never sitting still”. He built his political career empire while running the League’s Radio Padania and then embraced the digital era after becoming party leader by both closing the newspaper and shifting the radio online.

As Salvini campaigns it is clear his sights are as much set on courting support for his domestic politics as making pan-European gains. “If the League is the first party not only in Italy, but in Europe, then the music changes,” he said at a rally in Modena in early May.

But those who know him fear the country is being taken down a perilous path.

“He is making mistakes in foreign relations, says Giulio Sapelli, an economics professor who taught Salvini at the University of Milan. “The League needs to be a party of the centre, having optimal relations with Germany and France, instead of allying with people like Orbán and Le Pen.”

Davide Boni, an ex-League politician, agrees. “He puts himself forward as the strongman of Italy … but this is the kind of thing we’ll end up paying for.”

As for Salvini’s ultimate vision for Italy, it is difficult to gauge. “He isn’t a statesman, he lives off the polls,” says Boni.

Piazzo puts it more bluntly: “He wants power, and that’s it.”