It’s that time of year again, when many randomly claim to be Irish in a bid to find some excuse to celebrate Saint Patrick’s Day.

Of course, they could just join in anyway – it’s not like you have to have a deep and entrenched Chinese cultural heritage to raise a glass for the Year of the Rat, for example.

But Paddy’s Day is different, particularly for famous types in the USA who, no matter how tenuous the family link, still attempt to align themselves with the celebrated nationality of choice.

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For musicians, being of mixed cultural heritage is often touted as something of a USP. It’s what sets them apart from every other artist chucking out mediocre pop collaborations with Pharrell Williams or Calvin Harris (let’s face it, they have the monopoly on musical monotony right now).

“I’m an eighth Native American, two sixths Japanese, Zulu, German and part Nepalese Buddhist monk, but you know, I’m actually Irish, thanks to my sixth cousin thrice removed married in on my maternal side,” they’d probably say. Before mentioning an Italian grandmother and hence their insatiable appetite for ravioli. Or something.

Shape Created with Sketch. Bet You Didn't Know These Stars Were Irish Show all 21 left Created with Sketch. right Created with Sketch. Shape Created with Sketch. Bet You Didn't Know These Stars Were Irish 1/21 Jamie Dornan Dornan hails from County Down, Northern Ireland Getty Images 2/21 Peter O'Toole Peter O'Toole had two birth certificates - one from Yorkshire, and one from Ireland Getty 3/21 Dominic West Although he was born in Yorkshire, Mr West actually hails from a strong Irish Catholic background Getty Images 4/21 Michael Fassbender His mother is from County Antrim, Northern Ireland, and apparently the great-great niece of famed Irish revolutionary leader Michael Collins Getty Images 5/21 Emily Ratajkowski Model Emily Ratajkowski was born in London. Her father claims Polish-Irish ancestry Getty Images 6/21 Meryl Streep A researcher has claimed to have traced Streep's great-great grandmother Grace Strain's departure from Ireland to New York. Streep later named her daughter after the relative PA 7/21 John Travolta “The emotional, romantic, whimsical part of me is Irish," Travolta has been quoted as saying. Which apparently makes him a closet Paddy (WE SAID PADDY). 8/21 Christina Aguilera Genie in a Jameson bottle Christina Aguilera is no Dubliner, but like many Americans, claims she's Irish through her Irish-American mother. 9/21 Gwen Stefani Her surname's Italian, but did you know Gwen's mum was Irish? Neither did we. 10/21 Charlie Sheen Charlie's dad Martin is actually an Irish citizen, thanks to his mother Mary Ann Phelan's ancestry. 11/21 Robert De Niro Every nation tries to claim him as their own, it seems. But apparently De Niro has Irish roots. 12/21 Mariah Carey “My mother is Irish, my father is black and Venezuelan, and me — I’m tan, I guess.” She's also part dolphin, vocal rumours suggest. 13/21 Harrison Ford Yes, that's right Indiana Jones is in fact an Irishman. Well, half Irish. Thanks to his dad. 14/21 Ben Stiller Famously Jewish actor Ben Stiller is actually the son of an Irish-Catholic mum. 15/21 Alicia Keys "I’m definitely black and Italian and a little Irish," Keys confessed. 16/21 Barack Obama OK, so this is a long shot... But Barack Obama's great-great-grandfather was an Irish immigrant who left for America in 1850. So by American terms, the US President is a full blown Irishman. 17/21 Wayne Rooney Figures. He does have a head shaped a little like a potato. Thanks to Irish grandparents, Rooney is also eligible to play for the Irish squad, if he wanted to. 18/21 Rosario Dawson “I’m more Irish than anything," the Sin City star said about her cultural heritage. 19/21 Bruce Springsteen The Boss' great-grandmother, Ann Garrity, hailed from County Westmeath. 20/21 Tom Cruise Cruise was given a certificate of Irish heritage last year. He also played an Irishman in Far And Away. We'll let you make your minds up about that accent. 21/21 Leona Lewis The Irish frequently try to claim Hackney-dwelling X Factor champ Leona Lewis as their own, thanks to her mother's ancestry. 1/21 Jamie Dornan Dornan hails from County Down, Northern Ireland Getty Images 2/21 Peter O'Toole Peter O'Toole had two birth certificates - one from Yorkshire, and one from Ireland Getty 3/21 Dominic West Although he was born in Yorkshire, Mr West actually hails from a strong Irish Catholic background Getty Images 4/21 Michael Fassbender His mother is from County Antrim, Northern Ireland, and apparently the great-great niece of famed Irish revolutionary leader Michael Collins Getty Images 5/21 Emily Ratajkowski Model Emily Ratajkowski was born in London. Her father claims Polish-Irish ancestry Getty Images 6/21 Meryl Streep A researcher has claimed to have traced Streep's great-great grandmother Grace Strain's departure from Ireland to New York. Streep later named her daughter after the relative PA 7/21 John Travolta “The emotional, romantic, whimsical part of me is Irish," Travolta has been quoted as saying. Which apparently makes him a closet Paddy (WE SAID PADDY). 8/21 Christina Aguilera Genie in a Jameson bottle Christina Aguilera is no Dubliner, but like many Americans, claims she's Irish through her Irish-American mother. 9/21 Gwen Stefani Her surname's Italian, but did you know Gwen's mum was Irish? Neither did we. 10/21 Charlie Sheen Charlie's dad Martin is actually an Irish citizen, thanks to his mother Mary Ann Phelan's ancestry. 11/21 Robert De Niro Every nation tries to claim him as their own, it seems. But apparently De Niro has Irish roots. 12/21 Mariah Carey “My mother is Irish, my father is black and Venezuelan, and me — I’m tan, I guess.” She's also part dolphin, vocal rumours suggest. 13/21 Harrison Ford Yes, that's right Indiana Jones is in fact an Irishman. Well, half Irish. Thanks to his dad. 14/21 Ben Stiller Famously Jewish actor Ben Stiller is actually the son of an Irish-Catholic mum. 15/21 Alicia Keys "I’m definitely black and Italian and a little Irish," Keys confessed. 16/21 Barack Obama OK, so this is a long shot... But Barack Obama's great-great-grandfather was an Irish immigrant who left for America in 1850. So by American terms, the US President is a full blown Irishman. 17/21 Wayne Rooney Figures. He does have a head shaped a little like a potato. Thanks to Irish grandparents, Rooney is also eligible to play for the Irish squad, if he wanted to. 18/21 Rosario Dawson “I’m more Irish than anything," the Sin City star said about her cultural heritage. 19/21 Bruce Springsteen The Boss' great-grandmother, Ann Garrity, hailed from County Westmeath. 20/21 Tom Cruise Cruise was given a certificate of Irish heritage last year. He also played an Irishman in Far And Away. We'll let you make your minds up about that accent. 21/21 Leona Lewis The Irish frequently try to claim Hackney-dwelling X Factor champ Leona Lewis as their own, thanks to her mother's ancestry.

For American politicians, claiming to be part of the great Irish diaspora has entirely different motivations. For them, it’s a chance to associate themselves with the hard-working, family-orientated immigrants of the 1800s, who defied the odds when they settled in the States – a true, all-American success story of the underdog made champions through blood, sweat and sheer determination.

It’s also a chance to appeal to the 35.5million Americans – that’s 11.6 per cent of the population – who claim to have at least partial Irish ancestry. That’s five times as many Irish people in the USA claiming to be Irish than there is in Ireland.

According to American census data in 2013, they are most concentrated in the North East, particularly in the metros of Boston, where they make up 20 per cent of the population. New York State, New Jersey, Pennsylvania and New England are also heavy on the Irish side – and all are particularly influential States to canvas come election time.

So, who are these recognizable household names who, before St Patrick’s Day, you had no idea were Irish? Click through the gallery above to find out.

We guarantee almost all of them will surprise you.