That's the premise of "He's Back" ("Er ist wieder da"), a biting social satire by author Timur Vermes, the movie version of which premiered in German cinemas this week.
In the bestselling what-if novel published three years ago, Hitler is baffled to find himself in a multicultural Germany led by a woman, Chancellor Angela Merkel.
He discovers TV chefs, Wikipedia and the fact that Poland still exists before he ends up a small-screen star, in a social commentary on society, mass media and celebrity hype.
The film, however, goes a step further and sprinkles the story with documentary-style scenes -- in the style of Sacha Baron Cohen's 2006 comedy "Borat" -- giving the screen version a more disturbing twist.
In the real-life scenes, lead actor Oliver Masucci -- replete with Hitler moustache and uniform -- is seen getting rousing receptions from ordinary people, many of whom pose for "selfies" with him.
Tourists and football fans cheer the fake Hitler at Berlin's Brandenburg Gate, in a Bavarian village and elsewhere, and elderly people pour their hearts out to him, often voicing extremist views.
"Yes, bring back labour camps," says one citizen to the dictator.
Such scenes have touched a raw nerve in Germany which, amid a record influx of refugees, has also suffered an upsurge in xenophobic protests and attacks against asylum-seekers.
"There is a smouldering anger among the people, like in the 1930s," says the Hitler character, with visible satisfaction.
Masucci, best known as a stage actor, told Bild daily about his mixed feelings while shooting the unscripted scenes with people on the street.
"During shooting, I realised: I didn't really have to perform -- people felt a need to talk, they wanted to pour their hearts out to a fatherly Hitler who was listening to them," he said.
"I found it disturbing how quickly I could win people over. I mean, they were talking to Hitler."
Hitler in the film also meets members of the populist-nationalist Alternative for Germany party and the neo-Nazi NPD, while the final scenes show news footage of far-right mobs and a rally by the PEGIDA movement, short for "Patriotic Europeans Against the Islamisation of the Occident".
The release of the movie has touched off broad debate in a country where guilt over World War II and the Holocaust continues to influence political debate.
"A fake Hitler, a small moustache clearly helped people lose their inhibitions and... allowed insights into Germany's dark side," found the daily Berliner Morgenpost.
After all, it said, Hitler, in a figurative sense, "never really left".
"The far-right ideology smoulders to this day and has found new forums... in the form of the Alternative for Germany and the PEGIDA movement," it said.
A review by news portal Spiegel Online was more critical: "Borat with a bar-moustache and side parting: It sounds like a clever flick," it said. "But really it's rather silly.
"Because what would be an appropriate response from a passer-by to the Hitler masquerade? It reveals nothing, neither people's indifference nor their hidden sympathies."
Tagesspiegel daily pointed out that "Hitler sells", in a trend that has been dubbed the 'banalisation of evil' and has turned the monstrous historical figure into something of a commercialised pop icon.
"70 years after the end of the 'Third Reich', which left countries destroyed and millions dead, the dictator has shrunk to become a caricature, either loaded with nonsense or with meaning, in books, cinema, TV, Internet," it said.
At the public premiere Thursday, a Berlin audience roared with laughter during the funnier moments, but quietened during some of the real-life footage.
One viewer, who gave her name as Angela, thought "it was all a bit too forced. The film is playing too hard on the fear about Nazi ideology, and they only picked out the worst sequences."
Another viewer, Tobias, was more disturbed, given the real-life resurgence of the populist far-right.
"This is real," he said. "We need to debate this. It shows how easily people can be manipulated. This is the right moment, because the danger is here now."