Mila Kunis — Milena Markovna Kunis
At the age of seven, Milena Markovna Kunis and her family moved from Ukraine to Los Angeles, Calif.
Mila's mother, Elvira, and father, Mark, soon enrolled her in acting classes and allowed Mila to shorten her name when she started booking her first roles on "Days of our Lives," "7th Heaven," and playing a young Angelina Jolie in "Gia."
Joaquin Phoenix — Joaquin Rafael Bottom/Leaf Phoenix
Joaquin Rafael Bottom is the third of five children, all with equally interesting names, including River (1970–1993), Rain (1973), Liberty (1976), Summer, and a half-sister Jodean.
After Joaquin's parents, John Lee and Arlyn Bottom, married in 1969, the couple joined the religious cult the Children of God and traveled around South America. But they soon became disenchanted with the cult and moved back to the U.S. in 1978, where they changed their last name to "Phoenix" to symbolize "new beginning."
Around this same time, a young Joaquin began calling himself "Leaf," desiring to have a similar nature-related name like his siblings. In a past Jay Leno interview, Joaquin said he had originally called himself "Antleaf" as a child.
Leaf would become the name he would use as a child actor until, at age 15, he changed it back to Joaquin.
Reese Witherspoon — Laura Jeanne
The "Sweet Home Alabama" actress traded her first and middle name in for her mother's maiden name, "Reese."
Katy Perry — Kathryn (Katy) Hudson
Before she was a chart-topping singer, Perry was producing Christian music under her birth name, Kathryn Hudson. She released gospel record "Katy Hudson" under the former label Red Hill Records before adopting her mother's maiden name to avoid confusion with actress Kate Hudson.
Christopher Walken — Ronald Walken
According to a Salon article from 2000, Walken was originally named after actor Ronald Colman.
The change in name came about after singer Monique Van Vooren, whom Walken worked for at the time, renamed him Christopher for no real apparent reason. The name stuck, though his friends still call him Ronnie.
Natalie Portman — Natalie Herschlag
After being born in Jerusalem, Israel, in 1981 to an Israeli gynecologist father named Avner Hershlag and American mother named Shelley Stevens (her mother's family changed their last name from "Edelstein" to "Stevens" when arriving in the U.S. from Russia and Austria), Portman now holds dual American and Israeli citizenship.
Whoopi Goldberg — Caryn Elaine Johnson
The actress and "The View" correspondent didn't become Whoopi Goldberg until, while working in a theater in San Diego, friends noticed she had a bit of a flatulence problem and began calling her Whoopi after a whoopee cushion.
"If you get a little gassy, you've got to let it go," Whoopi has said. "So people used to say to me, 'You're like a whoopee cushion.' And that's where the name came from."
It was Whoopi's mother who felt her daughter should take a Jewish-sounding last name to advance her Hollywood career. And thus Whoopi Goldberg was born.
Louis C.K. — Louis Szekely
The comedian's Hungarian surname is pronounced SEK-kay; however, after people had a tough time pronouncing his name, he decided to change it to an easier English translation: SEE-Kay.
Miley Cyrus — Destiny Hope Cyrus
Cyrus' father Billy Ray gave her the nickname "Smiley" to match her cheery persona.
Over the years, the nickname became shortened to Miley. Cyrus legally changed her name in 2008.
Drake — Aubrey Drake Graham
When he played wheelchair-bound Jimmy Brooks on the Canadian TV show "Degrassi," the actor went by the name Aubrey Graham. But when the Toronto native switched his career focus to rapping in 2009 after signing a recording contract with Lil Wayne's Young Money Entertainment, he started using one name only: Drake.
Demi Moore — Demetria Gene Guynes
Moore kept the last name of her first husband Freddy Moore after they divorced in 1984.
Daughter Tallulah also legally changed her name to Lula. Father Bruce Willis first broke the news in 2007 on "The Late Show with David Letterman."
"She wanted me to mention here on the big show that she's legally changing her name from Talullah to Lula, just Lula," said Willis. "She doesn't like her name."
Jodie Foster — Alicia Christian Foster
Foster's estranged brother Buddy claims her name change to "Jodie" came as the result of a nickname, the code, "Jo D" for their mother's partner, Josephina Dominguez, in his book, "Foster Child: A Biography of Jodie Foster."
Jamie Foxx — Eric Marlon Bishop
Rumor has it Foxx picked an androgynous name because he noticed female comedians were often picked over men to perform at comedy clubs.
Tina Fey — Elizabeth Stamatina Fey
That's right. Fey shares the name of her "30 Rock" Liz Lemon character. Her stage name is just a shortened version of her middle name.
Ludacris — Christopher Brian Bridges
The rapper has said the stage name explains his split personality.
"The nickname is something I made up," said Ludacris. "Part of me is calm, cool, and collective (sic), while the other side is just beyond crazy."
Before becoming a rapper, Ludacris was known as "Chris Luva Luva" on Atlanta's Hot 97.
Meg Ryan — Margaret Mary Emily Anne Hyra
Born in Fairfield, Conn., to Roman Catholic parents named Susan Jordan and Harry Hyra, Margaret Mary Emily Anne Hyra changed her name to Meg Ryan after she dropped out of NYU one semester early to pursue her budding acting career.
Ben Kingsley — Krishna Pandit Bhanji
Kingsley revealed on "Inside the Actors Studio" he feared a foreign name could hurt his career.
Charlie Sheen / Martin Sheen — Carlos Irwin Estevez / Ramon Antonio Gerard Estevez
With his paternal grandparents originally immigrants from Spain and Ireland, Sheen wanted to take on a more American name. His children share the Sheen surname.
According to a 2003 "Inside the Actors Studio" interview, Martin Sheen revealed he took his name from CBS casting director Robert Dale Martin, who gave him his big break, and a Catholic televangelist, Fulton J. Sheen, whom he thought was a great actor. Unlike his son Charlie, Martin never legally changed his name.
Emilio Estevez (right), of course, kept his name.
Dakota Fanning — Hannah Dakota Fanning
The youngest nominee ever for a Screen Actors Guild Award, Hannah Dakota Fanning goes by her middle name professionally instead of her legal first name.
Fanning, whose mother Heather Arrington played professional tennis (her father, Dakota's grandfather, was NFL player Rick Arrington) and father, Steven Fanning, a former minor league baseball player, is of Irish and German ancestry.
Michael Caine — Maurice Joseph Micklewhite
In 2009, Caine explained re-naming himself after Humphrey Bogart's character in "The Caine Mutiny" to New York Magazine.
"Bogart was my hero, and even though he came from a sort of snobby, aristocratic family—he was a distant relation of Princess Diana—when I was a kid I thought he was a tough guy," said Caine. "Any person with my working-class background would be a villain or a comic cipher, usually badly played, and with a rotten accent. There weren’t a lot of guys in England for me to look up to."
Bono — Paul David Hewson
The U2 frontman and humanitarian we all know as Bono wasn't actually born with just one name. Before he became world famous, the Irish musician was known by the name Paul David Hewson. But his wife still reminds Bono of his roots, going by the name Ali Hewson.
The name Bono was originally a nickname, short for "Bono Vox" meaning "good voice" in Latin, said to be given by his friend Gavin Friday.
Lady Gaga — Stefani Joanne Angelina Germanotta
Stefani Joanne Angelina Germanotta was born and raised in New York City.
In the October 2013 issue of Elle magazine the singer said she changed her name because Stefani is "a perpetually tortured artist" that she can't be in public.
Chevy Chase — Cornelius Crane Chase
Cornelius Crane Chase was named after his mother's adoptive father, Cornelius Vanderbilt Crane, heir to the successful New York company, Crane Plumbing.
The nickname Chevy was given by his grandmother, from the medieval English "The Ballad of Chevy Chase." As a descendant of the Scottish Clan Douglas, she felt the name "Chevy" seemed fitting.
Portia de Rossi — Amanda Lee Rogers
The "Arrested Development" actress told advocate.com in 2005 she changed her name legally at the age of 15 to reinvent herself after coming out as gay.
The name Portia is from a Shakespearean character in "The Merchant of Venice." She chose an Italian last name:
"De Rossi because I was Australian and I thought that an exotic Italian name would somehow suit me more than Amanda Rogers. When you live in Australia, Europe is so far away and so fascinating, so stylish and cultured and sophisticated."
Natalie Wood — Natalia Nikolaevna Zakharenko
After being born in San Francisco to Russian immigrant parents in 1938, Wood Americanized her name when she became a child actress at just four years old.
At age eight, Wood starred in "Miracle on 34th Street" and went on to have a successful, Oscar-nominated acting career as an adult before mysteriously drowning near Santa Catalina Island in 1981 at age 43.
Vin Diesel — Mark Sinclair Vincent
The "Fast and Furious" star told Conan O'Brien on "Late Night" he changed his name while working as a bouncer at New York nightclubs. Vin is a shortened version of the actor's last name.
Diesel was a nickname from friends who said he ran on "diesel" fuel because he had so much energy.
Michael Keaton — Michael John Douglas
The "Batman" actor changed his name early in his career to avoid confusion with actor Michael Douglas and TV host Mike Douglas.
Though rumors have suggested he changed his name because he liked the sound of Diane Keaton's name, the actor told Grantland that wasn't true. He changed his name to join the union. It's believed he chose Keaton because of comedian Buster Keaton.
Fergie — Stacy Ann Ferguson
With Black Eyed Peas band mates named will.i.am, apl.de.ap and Taboo, the name Stacy Ferguson just wasn't going to cut it.
After being a member of the children's TV show "Kids Incorporated" and performing with the girl group "Wild Orchid," Ferguson quickly changed her name to something that would pop like her music: Fergie.
Spike Jonze — Adam Spiegel
The director of critically acclaimed "Her" got his pseudonym from co-workers of a Rockville BMX store because "he'd come to work without showering, and his hair was usually sticking straight up," according to New York Magazine.
Bruno Mars — Peter Gene Hernandez
Mars changed his Puerto Rican name "to avoid being stereotyped" into performing solely Latin and Spanish music, according to GQ.
Where did the name come from? Bruno was the nickname his father gave him at the age of two because he reminded him of his favorite wrestler Bruno Sammartino.
The singer told rap-up.com the last name was to give him an edge:
"I felt like I didn’t have no pizzazz, and a lot of girls say I’m out of this world, so I was like I guess I’m from Mars."