"My youngest son once asked me half-jokingly, 'Dad, are you really a traitor?' Because this was broadcast on the so-called public media. It was partly a joke, but partly it wasn't," Magyar told AFP.

Since he denounced alleged government corruption in an interview a year ago that quickly went viral, Magyar's popularity has surged. His conservative TISZA party now leads the ruling Fidesz in many polls ahead of elections next year.

But the 43-year-old has faced a relentless onslaught of negative stories since becoming the main challenger to Orban's 15-year rule, which includes a tight grip of the media.

- 'Tsunami of hatred and lies' -

Initially, the government -- repeatedly accused by critics of silencing all opposition, often through legislative changes that deprive them of funding or platforms -- dismissed Magyar, who was elected as an EU lawmaker last June. He was described as a man in a "hopeless situation".

But as his popularity grew, the airwaves started filling up with what Magyar described as "vile, Goebbelsian propaganda", referring to Nazi propaganda chief Joseph Goebbels, and a "tsunami of hatred and lies".

Derogatory stories include Fidesz politicians alleging he wears women's sunglasses to a TV report claiming he "touched his genitals" in the European Parliament.

He has ridiculed some claims, he has dismissed others, including accusations of domestic abuse of his ex-wife Judit Varga -- a former justice minister with whom he has joint custody of their three teenage sons.

In audio recordings leaked in recent months, he was also heard badmouthing fellow MEPs and supporters. Magyar claims these were manipulated with AI.

Magyar said he and his allies received threatening messages daily, warning those who want to join TISZA ahead of the party's first congress this weekend.

"Not only will they be viciously attacked, but their godchild and uncle, too," he said.

Orban rarely attacks Magyar -- a lawyer by training and former Brussels-based diplomat -- directly.

But Fidesz leverages its influence to conduct "extreme smear campaigns against its opponents", according to sociologist Andrea Szabo.

"They are slandering politicians personally rather than questioning their policies, which is more reminiscent of autocratic countries in the East than Western democracies," she told AFP.

But Magyar can mostly defuse smear campaigns because he "knows the mechanisms of this system well" and voters believe in his ability to bring about change, Szabo said.

Still, being always forced into a confrontative stance could damage his image in the longer term.

"This may plant the idea in people's minds, that there is always some problem with him, he would be unable to govern," the expert added.

Besides promising to fight graft, many of the policies Magyar proposes mirror Fidesz' conservative standpoints, including a hard line against migration, while he usually dodges questions on his position on LGBTQ rights.

Internationally, Magyar has been critical of Brussels "intervening in domestic affairs" and is against severing ties with Russia, echoing Orban, one of the Kremlin's few EU allies despite its invasion of Ukraine.

Other opposition parties decry him for embodying a "Fidesz-like mentality", often spreading falsehoods, smearing political rivals and not apologising -- claims he has denied.

- Toughing it out -

Ahead of next year's vote, the opposition leader expects more attacks and more "sham investigations" similar to the one he faces over an incident in June, where he is being probed for theft for taking away a phone from a man filming him in a nightclub.

The European Parliament is reviewing whether to lift his immunity in the case as requested by Hungary's chief prosecutor.

Fidesz "will stop at nothing" to keep power, Magyar warned.

For some of its members, "their freedom is at stake because an independent judiciary would hold them accountable for the crimes they have committed," he added.

Magyar admits the pressure has made him lose weight, and he said he barely sleeps through the nights, thinking how "to build a country Hungarian people deserve".

"Someone compared the situation to steel tempering: the more it gets tempered, the tougher and more flexible it becomes. That is how I feel," he said.