You think you know these celebrities? Well think again! Plenty of our all-time favourite famous faces haven't actually changed their names for plenty of different reasons. Maybe they needed a stage name, or went with their middle name, or just wanted a change altogether! Scroll through our gallery to see the real names behind these stars...
Alex Jones – Charlotte Alexandra Jones
The One Show presenter uses her middle name as her first. After welcoming her son Teddy, she spoke about the difficulty of choosing a name. "We're a bit behind on the whole name thing because we didn't know if we were having a boy or a girl," said Alex. "We thought, 'When we see him we'll know what he looks like', but actually it's really hard." The TV star often refers to her little boy – whose full name is Edward Alun Burrell Thomson – as Ted or Teddy.
Jools Oliver – Juliette Norton
The mum-of-five became Jools Oliver after marrying her husband Jamie Oliver. The TV chef has even named some dishes after his loving wife, including Jools' Favourite Beef Stew, but her real name happens to be Juliette!
Emma Stone – Emily Jean Stone
It took Emma a few times to finally settle on her stage name. When she was 16, she had to ditch her first name Emily after joining the Screen Actors Guild and discovering there was another girl who shared her name.
Speaking to W magazine, the Oscar winner said: "To ask a 16-year-old to pick a new name is really an interesting process because I was like 'I'm going to be Riley. My name is going to be Riley Stone.' And so my name was Riley Stone for about six months and I did a guest spot on Malcolm in the Middle and one day they were like, 'Riley, Riley,' and I had no idea who they were talking to and they were like, 'Hey, hey come on we need you on set.' And I was like, 'Oh I'm not Riley, I can't be Riley'." The actress finally settled on Emma because it was "closer to Emily".
Helen Mirren – Helen Lydia Mironoff
The actress was born to Kathleen 'Kitty' Alexandrina Eva Matilda and Vasily Petrovich Mironoff. Helen's father anglicised the family name to Mirren in the 1950s and changed his name to Basil Mirren.
Martine McCutcheon – Martine Kimberley Sherri Ponting
The actress was born in Hackney, London to her mother Jenny Tomlin. At the age of ten, Martine took her stepfather's surname after her mum married window cleaner John McCutcheon.
Katy Perry – Katheryn Elizabeth Hudson
The singer was born to Pentecostal pastors Mary Christine (née Perry) and Maurice Keith Hudson, but for her stage name, Katy chose to adopt her filmmaker uncle Frank Perry's last name.
Lady Gaga – Stefani Joanne Angelina Germanotta
The chart-topper got her stage name from one of her producers, Rob Fusari. Rob texted her the Queen song Radio Gaga but somehow 'Radio' was autocorrected to 'Lady'. The rest is history!
Dido – Florian Cloud de Bounevialle O'Malley Armstrong
On her birth certificate, the singer is Florian Cloud de Bounevialle O'Malley Armstrong, but Dido has always made it clear that Dido is now her real name and not simply a stage name. It derives from the mythical Queen of Carthage.
During an interview with The Observer, she explained: "To be called one thing and christened another is actually very confusing and annoying. It's one of the most irritating things that my parents did to me. ... Florian is a German man's name. That's just mean. To give your child a whole lot of odd names. They were all so embarrassing. ... I thought it was cruel to call me Dido and then expect me to just deal with it."
Ola Jordan – Aleksandra "Ola" Jordan
The former Strictly Come Dancing star was previously Aleksandra Grabowska before marrying fellow dancer James Jordan.
Olivia Wilde – Olivia Jane Cockburn
The actress derived her stage name from Irish author Oscar Wilde. She changed her surname at high school, choosing to honour the writers and journalists in her family, many of whom use pen names.
Reese Witherspoon – Laura Jeanne Reese Witherspoon
A little known fact about the actress – Reese is actually her mother's maiden name!
Kirk Douglas – Issur Danielovitch
The 102-year-old actor grew up as Izzy Demsky but legally changed his name to Kirk Douglas before entering the United States Navy during World War II. His actor son, Michael Douglas, takes his name.
Portia de Rossi – Amanda Lee Rogers
The actress adopted her current name at the age of 15 when she wanted to reinvent herself. Portia came from William Shakespeare's The Merchant of Venice.
Bono – Paul David Hewson
Bono got his nickname after his neighbourhood hearing-aid store Bonavox, which is Latin for 'good voice'. His friends started calling him Bono as a teen, and it's stuck ever since.
Bruno Mars – Peter Gene Hernandez
The Treasure singer was named after his father Peter Hernandez, but was nicknamed Bruno from a young age, after his dad remarked that he looked like professional wrestler Bruno Sammartino.
Bruno added Mars to his stage name when he was pursuing a musical career in California. "I felt like I didn't have [any] pizzazz, and a lot of girls say I'm out of this world, so I was like I guess I'm from Mars," he explained.
Tom Cruise – Thomas Cruise Mapother IV
The actor was named after his father Thomas Cruise Mapother III.
Whoopi Goldberg – Caryn Elaine Johnson
Unsurprisingly, the name Whoopi was taken from a whoopee cushion. "If you get a little gassy, you've got to let it go. So people used to say to me, 'You're like a whoopee cushion.' And that's where the name came from," the actress has said.
Of her surname, she said: "My mother did not name me Whoopi, but Goldberg is my name, it's part of my family, part of my heritage. Just like being black."
Iggy Azalea – Amethyst Amelia Kelly
The Fancy rapper took her stage name from the name of her childhood dog, Iggy, and the street she grew up on, Azalea Street, where her family lives to this day.
Joaquin Phoenix – Joaquín Rafael Bottom
The Walk the Line actor was born Joaquín Rafael Bottom, but for a period of time he was known as Leaf Phoenix.
Judy Garland – Frances Ethel Gumm
The Wizard of Oz star was named after her dad Francis and her mum Ethel. There are several stories around the change of her name. She is said to have picked Judy after being inspired by a popular Hoagy Carmichael song, while Garland came from Carole Lombard's character Lily Garland in the film Twentieth Century.
Martin Sheen – Ramón Antonio Gerardo Estévez
The actor adopted his stage name after claiming that people became suspicious of his birth name. He explained: "Whenever I would call for an appointment, whether it was a job or an apartment, and I would give my name, there was always that hesitation and when I'd get there, it was always gone. So I thought, I got enough problems trying to get an acting job, so I invented Martin Sheen.
It's still Estevez officially. I never changed it officially. I never will. It's on my driver's license and passport and everything. I started using Sheen, I thought I'd give it a try, and before I knew it, I started making a living with it and then it was too late. In fact, one of my great regrets is that I didn't keep my name as it was given to me. I knew it bothered my dad."
Meg Ryan – Margaret Mary Emily Anne Hyra
The actress' birth name is a lot longer than her stage name!
Michael Caine – Sir Maurice Joseph Micklewhite Jr. CBE
The actor was named after his father Maurice Joseph Micklewhite Sr., a fish market porter.
Shania Twain – Eilleen Regina Edwards
The Man! I Feel Like a Woman! singer was born Eilleen Regina Edwards. She legally took her stepfather's surname Twain after she was adopted by him at a young age, when her mother remarried.