Beaming before an exultant sea of people in central Dublin, U.S. President Barack Obama on Monday revelled in his distant Irish ancestry, offering spirited thanks from tens of millions of Americans who trace their own connections to Ireland.

With his wife, Michelle, at his side, the president told many thousands who had gathered: "We feel very much at home."

In a speech devoted as much to personal pride than overt politics, Obama said he had come to reaffirm the bonds of affection between the United States and Ireland.

"There's always been a little green behind the red, white and blue," he said to cheers.

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Barack Obama drinks a pint of Guinness beer on Monday as he meets with local residents at Ollie Hayes pub in Moneygall, Ireland, the ancestral homeland of the U.S. president's great-great-great grandfather. (Pool/Associated Press)

Obama spoke shortly after he had downed a pint of Guinness in tiny Moneygall, the small Irish village where his great-great-great grandfather once lived and worked as a shoemaker.

It was an improbable and memorable pilgrimage for America's first black president into his Irish past, and Obama soaked it in.

O'Bama?

"My name is Barack Obama, of the Moneygall Obamas," the president said. Then, playing off the popular Irish spelling of surnames — O'Bama — the president said, "I've come home to find the apostrophe that we lost somewhere along the way."

The president struck a more serious tone in marking the adversity of Ireland's history and current times, celebrating a country that shares a resilient success with America.

"We're peoples, the Irish and Americans, who never stop imagining a better future, even in bitter times," Obama said.

Obama addressed roughly 30,000 people packed into College Green for an open-air event billed as a celebration of Irish culture.

Irish Prime Minister Enda Kenny introduced the Obamas to a crowd that made clear its desire that he step aside for their distinguished guest as quickly as possible. "Obama!" they chanted as Kenny, undeterred, continued to proclaim the inspiration of Obama's life story.

"The 44th president is different, because he doesn't just speak about the American dream — he is the American dream!" Kenny said before surrendering the podium to thunderous cheers.

Ash cloud

Obama was originally to spend the night in Dublin before flying to London on Tuesday. But an approaching ash cloud from an Icelandic volcano has forced the crew of Air Force One to move up that flight. 

Obama and wife Michelle arrived in London well ahead of schedule. Air Force One touched down in London late Monday. They are on an official state visit at the invitation of Queen Elizabeth.

The president plans to meet with British Prime Minister David Cameron to discuss a range of international issues, including Libya and Afghanistan.

Obama will then travel to Deauville, France, to meet with the heads of leading industrial nations before ending his trip with a visit to Poland, a strategically important Central European ally.

An overarching theme of Obama's trip — his eighth to Europe since taking office — will be to reassure the region that it still has a central role in U.S. foreign policy, even though Obama has put a premium on boosting U.S. relations with Asia and emerging markets elsewhere in the world.