When he became the European Union's top official, he hardly spoke any English, so he couldn't communicate directly with leaders of most EU nations. He also never held any previous international position. Until he was well in his 20s, he wasn't even able to travel out of his native Poland.
However, as President of the European Council, Mr Donald Tusk is now expected to coax and cajole leaders of the EU's 28 member- states into dealing with some of the continent's most intractable problems. And the 59-year-old has to do this with no formal powers, apart from those of persuasion and improvisation.
Mr Tusk seems to have been fated to be an unusual politician. He was given a British first name because a century ago his grandmother fell in love with a British nobleman called Donald and wanted each family generation to bear that name.
In a Poland that is one of Europe's most homogenous nations with almost 97 per cent of the population classified as ethnic Polish, Mr Tusk hails from the tiny Kashubian ethnic minority, a little-known group of only 250,000 souls with its distinct history, culture, language and even flag. And politics was always his vocation, despite the fact that his youth was spent under a communist regime which crushed any political activity.
For a while, it appeared that he would fulfil none of his dreams.
Barred from government employment because of his anti-communist activities, Mr Tusk and his wife, whom he met and married at university, ran a small industrial painting business, in defiance of the communist authorities' hostility to the market economy.
The collapse of Poland's communism in 1989 gave Mr Tusk the opportunity he craved. He founded two consecutive political movements and although the first one failed, by 2001 he was in charge of the Civic Platform, a centrist party which in 2007 propelled him to power as Prime Minister. He held the position for the next seven years, the longest such period in his country's democratic history.
"It was hard work, 16 hours a day, under the beating sun," recalled Mr Jerzy Borowczak, a close friend.
But the collapse of Poland's communism in 1989 gave Mr Tusk the opportunity he craved.
He founded two consecutive political movements and although the first one failed, by 2001 he was in charge of the Civic Platform, a centrist party which in 2007 propelled him to power as Prime Minister. He held the position for the next seven years, the longest such period in his country's democratic history.
He used his power well, by freeing Poland from the entrapments of its tragic past, which overshadowed generations of previous politicians.
He forged a close relationship with Germany, still resented by many Poles for the role it played in Poland's destruction during World War II. He also extended a friendly hand to Russia, another neighbour Poles deeply mistrust. And he consolidated Poland's spectacular economic progress - the nation is now three times richer than it was when communism collapsed.
The decision of fellow EU heads of government to elect Mr Tusk as EU leader on Dec 1, 2014 was, therefore, not only a personal triumph, but also a historic victory for Poland; it was the most prestigious international job given to a Pole since Karol Wojtyla became Pope John Paul II in 1978.
The crisis which preoccupied the EU at that time - the Russian military intervention in Ukraine - also played to Mr Tusk's strengths; his presence in Brussels reassured fellow former communist countries of Eastern Europe that their fears about Russia were understood.
Yet in handling all the subsequent crises, from Greece's financial disaster to Britain's renegotiation of its EU membership and the waves of migrants now hitting Europe's shores, Mr Tusk found himself in uncharted territory.
His job is, essentially, that of ensuring that EU heads of state and government keep talking and take the right decisions at the right time. That means sometimes the best policy is, literally, to lock leaders up.
"Sorry, but you are not leaving this room" is what he told German Chancellor Angela Merkel and Greek Prime Minister Alexis Tsipras as they were prepared to admit defeat after 14 hours of fruitless talks on the Greek crisis last year. It was a simple appeal to reason which averted a European disaster: Greece was saved from bankruptcy.
At other times, it fell to Mr Tusk to take action, since no one else would. He was instrumental in drafting the package of concessions that has allowed Prime Minister David Cameron to argue that Britain should remain in the EU. Without Mr Tusk's draft paper, the negotiations would have gone nowhere.
Although he could not directly address the political passions sparked by Europe's current immigration crisis, he did his best to ensure that these did not paralyse EU decision-making.
His visits to southern European countries, which act as conduits for migration flows, were an essential preparation to a crucial EU summit on migration which starts today .
His progress has not been trouble-free. His party did not survive his departure and was resoundingly defeated last year. And in Brussels, some officials dismiss his low-key style, which eschews media-friendly smiles and the public backslapping so favoured by other European leaders.
Nevertheless, Mr Tusk delivered on what he set out to do. After decades of west European domination, he proved that east Europeans can provide the EU with an equally authentic voice. He kept the EU working, notwithstanding mounting crises. He also honoured his promise to learn English.
And he is certainly a more substantial figure than another Donald now hogging the limelight on the other side of the Atlantic.