From a Special Forces soldier in 1999's "Three Kings," an adventurous sea captain in "The Perfect Storm," a suave con artist Danny Ocean in "Oceans 11," to CIA agent in the political thriller "Syriana," he's transformed himself into countless leading roles.
"I was just as stunned as anybody watching it, to see how he did that," father Nick Clooney said. "He undertakes another character and I said, where'd he get that?"
George Clooney is nominated for best actor for his role as corporate hatchet-man Ryan Bingham in "Up in the Air." It's the star's fifth Academy Award nomination. He won best supporting actor in 2005 for "Syriana."
But before he became one of Hollywood's biggest stars, the Oscar-winning actor was another nerdy-looking kid in glasses. People magazine's two-time choice for "Sexiest Man Alive" went through an awkward stage in middle school like everyone else.
"George and his glasses, an experiment that did not work out," his dad joked.
Watch "Before They Were Famous," on a special edition of "20/20" tonight at 10 p.m. ET
Nick Clooney took "20/20" on an exclusive tour of the family house in Augusta, Ky., that his mega-famous son calls home.
Clooney grew up in Augusta with parents Nina and Nick Clooney and older sister Ada. From a young age, his father could sense that his goofy, outgoing son would become a performer.
"I was sure that he would in one way or another be in a public profession because he just had that knack," he said. "He could contact people and he could make them laugh ...and he was just very interested in performing."
Clooney, an impressionable son, often visited the TV station in Lexington, Ky., where his dad worked as a newscaster and talk-show host, and picked up the lingo without a hitch.
"When George was two, three years old, he got laryngitis. Scared him to death. He came running to his mother, saying, 'Mom, mom, I'm having audio difficulties,'" Nick Clooney said.
His father's job as a newsman instilled an interest in current events and social activism in the boy, which he has carried into adulthood.
"We would talk around the dinner table or the breakfast table or particularly on the weekends when we had more time to spend together. We would talk about whatever was going on in the world," Nick Clooney said. "We would talk about the history of our communities and what were the problems and how they might be solved."
Clooney has used his star power to bring awareness to international crises, including the conflict in Darfur, and last month, organizing a "Hope for Haiti" telethon to help victims of the Haiti earthquake. In 2008, he became a United Nations Messenger of Peace.
Clooney was an outgoing, charismatic, and optimistic teen, his dad said.
At 13, he developed Bell's palsy, a temporary form of facial paralysis caused by damage to the cranial nerve. For several months, half of his face was paralyzed.