It's a daunting prospect, playing a legendary character who for decades has been associated with a much-loved actress.
So it's no surprise Emily Blunt had a moment of dread when she was asked to play Mary Poppins in the long-awaited sequel to the classic Julie Andrews film.
But she quickly realised she had to tackle the role her own way and not try to copy her predecessor.
"No-one can out-Julie Julie Andrews, so I had to do something that felt organic and representative of what I had taken from the books. Even though I had seen the film as a child, I decided not to watch it when prepping.
"She [Mary] was so clear to me from reading that I decided not to be intimidated by the iconic Julie Andrews in the role and just approach it as I would any other part."
Emily's Mary in the movie Mary Poppins Returns is based more on the character in PL Travers' books, and is more vain, capricious and enigmatic than the Julie Andrews version in the 1964 film.
"She thinks she is better than everyone else – which she is."
Emily also used a fast-talking journalist portrayed by Rosalind Russell in the 1940 comedy film His Girl Friday as inspiration. "She's like a tornado," explains Emily. "I went, 'That's it, that's the pace'."
Filming the movie had its challenges. Scenes of Mary flying into London on the end of a kite involved Emily (35) being suspended from a crane.
"I was about 50 feet in the air, having to look effortless," recalls Emily, looking a little queasy at the memory.
She also had to learn how to dance – a skill she's not particularly proficient at.
Luckily, singing wasn't a problem. Emily has a beautiful voice that was first showcased in the 2014 movie musical Into the Woods.
But she kept so quiet about her ability that even her husband, actor John Krasinski, had no idea she was so talented.
"I had literally never heard her sing a note," says John, who played Jim Halpert on the US version of The Office.
So when he stopped by the studio where she was performing her parts on the soundtrack, he was in for a shock.
"Emily started singing and I immediately wept," says John (39). "It was really wild. It was like finding out that your wife can levitate. It was like, 'When were you going to tell me this?'"
A career in entertainment was never on the cards for Emily when she was growing up in London, although her mother was a theatre actress turned language teacher. Instead, she planned on being an interpreter.
But developing a stutter when she was a child took her down a completely different path. Not only did she start drama lessons, but she became adept at imagining what it was like to be other people.
"Because I couldn't speak fluently, I watched and listened. I'd be on the Tube and I'd wonder about people and invent back stories for everyone. There's always been a natural desire to walk in the shoes of others."
Acting helped her to speak freely, she says.
"It was the tool I had to speak properly. I was that kid, upstairs in my room, trying out stuff in the mirror. But I'd never tell anyone about it."
However, it's hard to hide talent when it's as impressive as Emily's.
A school production she performed in was chosen for the prestigious Edinburgh Festival, where she was spotted by an agent who signed up the somewhat reluctant teenager.
"I didn't have a desire to pursue acting and I wouldn't have if I hadn't fallen into it. Crazy, isn't it? But that's probably why I ended up booking jobs, because I didn't have any nerves."
Her first professional stage role, at 18, was playing Dame Judi Dench's grand-daughter in a play called The Royal Family.
She won a Best Newcomer award and forged a firm friendship with Judi, who to Emily was the perfect example of a proper leading lady.
"She taught me everything about how to be gracious and graceful, and not take it seriously. She showed me how I wanted to be for the rest of my career."
Emily went on to find silver-screen success in movies like The Devil Wears Prada, The Girl on the Train and A Quiet Place. Mary Poppins Returns looks set to make her even more famous, but that's not a goal Emily particularly strives for.
While she loves her work, she is also equally happy to rush home to daughters Hazel (4) and Violet (2). She even jokes about "flipping" homes for a living as being a dream job that wouldn't take her away from her family so much.
Should the day come when Emily's no longer getting exciting roles, then she might just change careers, she smiles.
"Once I begin playing everyone's mother, then I'll just start flipping houses instead."