KRISTINEHAMN, SWEDEN - Kimmie Ahlen was once seduced by the violent underpinnings of neo-Nazi ideology, but today, alarmed by the spread of populism, he has a new mission - teaching tolerance to young Swedes.

With a blond buzz cut, piercing blue eyes and beefy shoulders chiseled in the gym and boxing ring, Ahlen makes an imposing impression.

The young boy who was once teased by his classmates is long gone, transformed by muscles and tattoos on his fingers and neck.

At an age when most students were enjoying their first flirtations and struggling through book reports, he joined a gang of neo-Nazi skinheads immersed in Nordic mythology and Holocaust denial, convinced of the superiority of the "white race". Many of them were criminals and drug addicts.

But that was then.

Now 27, Ahlen spends his time warning teenage students in Sweden about the dangerous allure of hatred, in a country of 10 million that has taken in almost 300,000 migrants since 2014.

"The world is different today. Donald Trump is president of the United States and the Sweden Democrats may soon take power in our country," he said in an interview with AFP, referring to the country's far-right party.

Childhood

A municipal youth councilor, he lives alone in a red-and-white cabin on the shores of Lake Vanern, Sweden's biggest lake. Three hours southwest of Stockholm by car, it is an ideal spot for meditation and reflection.

As a shy boy, Ahlen was bullied at school by his classmates and even by some teachers. In his free time, he collected objects he found on the ground.

One day, when he was 12, he stumbled across a CD by Ultima Thule, a Swedish white-power rock group popular among neo-Nazis. It was a revelation.

"I loved the music," he said. "What really appealed to me was the way they spoke about Sweden. It made me patriotic, a National Socialist, without understanding the significance of nationalism at all."

However, during a stint in jail for theft, Ahlen met a Swedish teacher who helped him to turn the page on racism for good. For the first time, Ahlen felt as though someone was really listening, and he started talking.

At the insistence of his former boxing instructor, he gave his first speech for youths, the beginning of his social work.

In his eyes, exclusion is what pushes young people toward harmful behavior.

"You have to show them tolerance and talk to them, instead of closing the door and leaving a whole group on their own to burgeon and grow even more hateful and violent and dangerous."