Perry, who became famous for her hit singles "Ur So Gay" (2007) and "I Kissed a Girl" (2008) was actually a gospel singer before turning to the glittery world of pop. (Photo by Kevin Winter/Getty Images for VH1)
Relatively Unkno...Miley Cyrus, Bradley Cooper and Anne Hathaway are just a handful of megastars who weren't even a blip on Hollywood's radar in the year 2000.
It's hard to believe, but 20 of today's biggest celebrities were unheard of 10 years ago. Find out who they are ...
Miley CyrusToday we know about every Salvia trip Miley takes, but 10 years ago she wasn't even famous. It wasn't until "Big Fish" in 2003 that Miley, then credited as Destiny Cyrus, appeared on the big screen and from their embraced the role of Hannah Montana and ultimately became a pop superstar. (AP Photo/Chris Pizzello)
Justin BieberToday the world may belong to Justin Bieber, but in 2000 the Canadian pop star was only 6 years old. (Photo by Carlos Alvarez/Getty Images)
Sam WorthingtonAfter almost a decade of roles in Australian TV shows and films, Worthington gained some attention for his role as Marcus Wright in 2009's "Terminator Salvation." Since then the Aussie hunk has landed parts in "Avatar," "Clash of the Titans" and "Call of Duty: Black Ops."
Megan FoxAside from her role in "Bad Boyz II" as "Stars-and-Stripes Bikini Kid Dancing Under Waterfall," we didn't know Megan Fox until 2004's "Confession of a Teenage Drama Queen" opposite a Disney-era Lindsay Lohan. (Photo by Joe Scarnici/Getty Images)
Bradley CooperCooper was pratically a nobody in his first film, "Wet Hot American Summer" in 2001. Fast-forward to today and "The Hangover" star is one of Hollywood's new leading men. (Photo by Stephen Lovekin/Getty Images)
Emma StoneEmma Stone appeared in a handful of TV shows beginning in 2005, but didn't make it to the big screen until 2007's "Superbad" as Jonah Hill's crush Jules. Since then, she's quickly become everyone's crush. (Photo by Toby Canham/Getty Images)
Robert PattinsonIs it hard to remember a time when you weren't drooling over RPatz? Well, it had to be before 2005, because that's when his role as Cedric Diggory in "Harry Potter and the Goblet of Fire" came into existence. Prior to that Pattinson had only appeared in TV movies. We've never been so grateful for wizards and muggles. (Photo by Jason Merritt/Getty Images)
Taylor SwiftTaylor Swift has been so successful over the past few years, it's hard to believe she's only 21 years old. (AP Photo/Richard Drew)
Kanye WestWest released his debut album "The College Dropout" in 2004 before that the larger-than-life personality wasn't on the musical radar. (AP Photo/Jason DeCrow)
Blake Lively"Sisterhood of the Traveling Pants" was the best thing to ever happen to Blake Lively (and us). If it weren't for that coming-of-age story in 2005, we might never have been introduced to the "Gossip Girl's" Serena van der Woodsen, "The Town's" Krista Coughlin or "Green Lantern's" Carol Ferris. ( AP Photo/Stuart Ramson)
Katy PerryPerry, who became famous for her hit singles "Ur So Gay" (2007) and "I Kissed a Girl" (2008) was actually a gospel singer before turning to the glittery world of pop. (Photo by Kevin Winter/Getty Images for VH1)
Kim KardashianKim married music producer Damon Thomas in 2000, but we didn't even know her name back then. It really wasn't until 2007's racy tape with Brandy's younger brother RayJ that we were introduced to today's biggest reality TV starlet, Kim Kardashian. (Photo by Kevin Winter/Getty Images)
Olivia Wilde"Tron" star Olivia Wilde didn't break on to the scene until 2004 as a guest star on "The O.C." Who knew she would beat out Mischa Barton and Rachel Bilson to become Hollywood's "It Girl?" (Photo by Frazer Harrison/Getty Images)
RihannaThe 22-year-old R&B star from Barbados didn't release her first studio album until 2005, yet somehow we feel like we've been singing along with her for years. Oh na na ... (Photo by Bryan Bedder/Getty Images)
Lady GagaLady Gaga's debut studio album "The Fame" in 2008 made her a household name, but before that Stefani Joanne Angelina Germanotta was enrolled at New York University's Tisch School of the Arts and spent her free time performing on the Lower East side of Manhattan. (AP Photo/Matt Sayles)
Daniel RadcliffeThere's a good chance Radcliffe will forever be know as Harry Potter, but he didn't appear in the role until 2001. (AP Photo/Evan Agostini)
Carrie UnderwoodIt's been reported that Capitol Records was preparing a contract for Underwood but was forced to cancel it when company management changed in 1996. Because of this twist of fate we weren't introduced to the Country cutie until her "American Idol" audition in 2004 and subsequent win in 2005. (AP Photo/Wade Payne)
Anne Hathaway"The Princess Diaries'" Mia Thermopolis was Anne's first major role in 2001. She's come a long way from that frizzy-haired, awkward adolescent. (AP Photo/Chris Pizzello)
John MayerJohn Mayer's first studio album, "Room for Squares" was released in 2001. Prior to that, Mayer studied at Berklee College of Music in Boston before moving to Atlanta in 1997 where he amassed a strong fan base. (AP Photo/Evan Agostini)