US President Barack Obama and his wife Michelle landed aboard Air Force One as wind and rain whipped across Dublin airport, launching his most comprehensive European tour in two years, which also takes in Britain, the G8 summit in France and Poland.
"It is heartwarming to be here," said Obama, quipping that arrangements had been made for the sun to come out as he came into land.
The highlight of the overnight Ireland stay was a pilgrimage by the Hawaii-born son of a Kenyan father and white American mother to the tiny village of Moneygall, home of Obama's great-great-great grandfather.
The 350-odd residents of Moneygall in County Offaly, which has just a few shops and two pubs, have been looking forward to the US leader's visit -- expected to last just an hour -- for months.
Obama's eighth cousin, 26-year-old accountant Henry Healy, was buzzing with excitement.
"This is going to be one of the most historic days we have ever seen," he told AFP.
After meeting Irish President Mary McAleese and Prime Minister Enda Kenny, Obama hailed last week's visit to Ireland by Britain's Queen Elizabeth II, and said Northern Ireland's peace drive sent a "ripple of hope" around the world.
"I wanted to just express to the Irish people ... how inspired we have been by the progress that has been made in Northern Ireland," Obama said.
"It speaks to the possibility of peace and people in longstanding struggles being able to reimagine their relationships.
"To see Her Majesty the Queen of England come here ... sends a signal, not just in England, not just here in Ireland, but around the world."
The queen last week laid historic enmities to rest with the first trip to the Irish Republic by a British sovereign since independence in 1922.
The president was also due to deliver one of his trademark emotive speeches to thousands of Dubliners in a high-security outdoor event from the steps of the Bank of Ireland, against a backdrop of famed Trinity College.
A crowd of 20,000 was expected at a vast street party boasting acts including Westlife, the Sawdoctors and Irish Eurovision stars Jedward among the performers.
Actor Daniel Day-Lewis, Ireland rugby star Brian O'Driscoll and football hero Robbie Keane were also to appear.
Obama earlier told Kenny he was pleased with the progress Ireland was making after an economic meltdown that necessitated an International Monetary Fund and European Union bailout.
"It is a hard road, but it's one that the Irish people are more than up to the task to achieve," he said.
"We are rooting for Ireland's success and we will do everything we can to help them on the path to recovery."
The president's visit will also take him on a state visit to Britain, the G8 summit in France and to Poland, with a heavy focus on Afghanistan, the NATO operation on Libya and the debate over the next chief of the IMF.
Obama's great-great-great grandfather on his mother's side Falmouth Kearney, the 19-year-old son of a shoemaker, emigrated more than 160 years ago, arriving in New York in search of a better life.
Parts of the Kearney house are still standing, while an upper floor has been added on the pebble-dashed, two-bedroomed home.
A song celebrating Obama's distant Irish heritage is also doing the rounds.
"O Leary, O'Reilly, O'Hare and O'Hara, There's no one as Irish as Barack O'Bama," goes the ditty by the Corrigan Brothers.
"He's as Irish as bacon and cabbage and stew. He's Hawaiian, he's Kenyan, American too," it goes on.