Donald Tusk has it in him to be a bit of a hooligan. His younger self, he admits, would “roam the streets cruising for a bruising” to break the monotony of communist life in his home-town of Gdańsk, the port city on Poland’s Baltic coast.

Contrary to the image of the typical bloodless Brussels Eurocrat, the president of the European council, who stands alongside Jean-Claude Juncker as the most senior of EU figures, is a man of passion with a feel for who is on the right side of history. Last week it was frustration, not boredom, that brought out the inner wrecking ball.

“By the way,” said Tusk, at a press conference in Brussels with the Irish PM, Leo Varadkar. “I’ve been wondering what that special place in hell looks like, for those who promoted Brexit, without even a sketch of a plan how to carry it out safely. Thank you.”

“They will give you terrible trouble in the British press for that,” muttered Varadkar as the two men shook hands. “I know, I know,” Tusk responded, and smiled.

Donald Franciszek Tusk was born in April 1957 to a Kashubian family, a west Slavic ethnic minority of 300,000 people whose loyalty was neither trusted by the Nazis when they invaded Gdańsk, nor later Stalin.

His maternal grandmother was German, yet he grew up with tales of his relatives being taken to Nazi labour camps. The Russians were the liberators who didn’t leave, imposing a life of grinding tedium and poverty. Tusk learned to appreciate Europe’s complexity early.

When Tusk was 14, with his carpenter father in the grip of terminal illness, the Polish people rose up. He watched from the family home as the police and army opened fire on the protesters, public buildings burned and tanks rolled on to the blood-stained streets. Tusk was left with the opinion that those who are beaten are often the ones in the right.

He has described his late father as “very strict, a strong person, if you know what I mean”, and his mother, Ewa, who died in 2009, as “pure goodness”. But young Donald was headstrong, first running with the local football hooligans, and then in 1976 at the university of Gdańsk with the students rising up around the anti-communist trade union Solidarność, or Solidarity.

His first paid job was as a journalist for a Solidarity publication but he was forced into hiding with his pregnant wife Małgorzata in 1981 when the Moscow-backed leader General Wojciech Jaruzelski brought in martial law. Work was found as a bread seller and later as a labourer specialising in high altitudes with the aid of climbing equipment. The political activism continued for which he was arrested and briefly imprisoned. Fortunately, three days after being taken the regime announced an amnesty for political prisoners as it struggled to keep its grip.

Donald Tusk meeting prime minister Theresa May in Brussels last week. Photograph: Anadolu Agency/Getty

At the time of the collapse of communism in Poland, Tusk was the co-founder of the illegal monthly Political Review, propagating economic liberalism and liberal democracy. It would be the basis for his political career, initially as leader of a free-market pro-Europe party, the Liberal Democratic Congress, and then a key player in the centrist Civic Platform, as head of which he was that led to him becoming Polish prime minister from 2007 for a record seven years, during which the country enjoyed a period of unrivalled economic growth.

But his success earned him enemies, not least Jarosław Kaczyński, leader of the now ruling right-wing nationalist Law and Justice party, whose poisonous personal grudge still dogs Tusk at home. Kaczyński holds him responsible for a plane crash on 10 April 2010 that killed his brother, the then Polish president, Lech Kaczyński, a claim Tusk has dismissed as obviously politically motivated.

Tusk had run out of road at home. It was with the backing of the German chancellor, Angela Merkel that he was appointed by the 28 member states as president of the European council in 2014, a mediating, compromise-finding, role with a monthly salary of €32,200 (£28,180).

The contrast with the previous president, the former prime minister of Belgium, Herman van Rompuy, has proven stark. Rompuy, a Haiku lover known as “the Belgian submarine” for his understated style, brought a technical economist’s eye to a crisis. Tusk, a keen user of Instagram and Twitter, on the encouragement of his daughter, Katarzyna, brings an eye for the global picture. And, despite his relaxed style in his office, where he often dispenses with suit and tie, he has a firm belief in the need at times to apply some muscle.

In July 2015, Merkel and the Greek prime minister, Alexis Tsipras, could see no way through after 14 hours of talks over the crisis that looked set to end in Grexit. “Sorry, but there is no way you are leaving this room,” Tusk told them.

The past five years have seen Russia’s illegal annexation of Crimea, the migration crisis and the rise of Donald Trump, of whom Tusk has been an outspoken critic. But it will be Brexit that surely defines the Tusk legacy. As an aide says: “For him, Brexit is a catastrophic breach of the liberal democratic order that he fought for as a young man, an unravelling of everything he believes in.”

Not everyone in Brussels is convinced the comments last week were wise. But, confronted by May on Thursday, Tusk did not budge: “He remains of the view that while the truth may be more painful, it is always more useful”.