Long before the blonde beauty was saving lives on "Grey's Anatomy" or getting "Knocked Up," she was just your average alien attending high school at Roswell High.
Heigl found small screen success on the 1999-2002 WB hit series "Roswell" where she played Isabel, a stranded alien whose spaceship crashed in 1947 in Roswell, New Mexico. She, her brother Max (Jason Behr) and their friend Michael (Brendan Fehr) have been stuck ever since, concealing their true identities in 17-year-old bodies.
Since her days as a sexy alien, Katherine has stolen the silver screen in flicks like "27 Dresses," "The Ugly Truth," "Life as We Know It" and "New Year's Eve."
Katherine's had just as much success in her personal life – Heigl wed singer Josh Kelley in 2007 and the pair has two adopted children together.
Have the rest of her “Roswell” costars fared as well? Click “Launch Gallery” above to see the cast then & now!