When CBS’ "The Big Bang Theory" premiered in 2007, Kaley Cuoco captured fans’ hearts as neighbor-to-the-nerds Penny, a character she says is a lot like herself. "She’s just so loud and basically like me," she told ET Online. "She’s all over the place…"

But you don’t get a permanent spot on a sitcom that goes on for 12 seasons — and win multiple awards for your performance — without serious acting chops. Cuoco may have appeared to be a naïve newcomer when she first showed her sweet and smiling face on "The Big Bang Theory," but like her character, she put years of work into honing her skills, defining her goals, and finally, reaching them. And it all started when she was only five years old.

"I basically grew up on stages and grew up in front of the camera, and I always kind of loved it," she told Sidewalks. "My parents said, ‘Do it or don’t.’ It was never a big deal. … It was like another activity that we did. … It just kind of kept happening, and I kept working."

Acting was a fun pastime for Cuoco as a youngster, but over time, she started landing high-profile parts. Here’s how she grew from a child actor into her most famous role to date.

She’s worked since the beginning

Kaley Cuoco had plenty of interests as a child. She played tennis from age three, and she also enjoyed modeling and acting. Some of her earliest commercials were for Barbie and Oscar Meyer, when she was about five years old.

Her television debut came in 1992, when she was cast as Connie Reinhardt in a made-for-TV movie. "Quicksand: No Escape" told the story of a man who is framed for murder. At just seven years old, she joined an amazing cast, including Donald Sutherland, Tim Matheson, and Felicity Huffman.

From there, Cuoco’s career was set in motion, and she began landing roles on some of the decade’s most popular shows. In 1994, she appeared in an episode of CBS’ "Northern Exposure." She also had a guest spot on ABC’s "My So-Called Life." Two years later, she was on ABC’s "Ellen," playing a young version of Ellen DeGeneres’ character.

Chasing her big break

By the time she was a teenager, Cuoco was a nationally ranked tennis player. She also took up horseback riding. But she was onto something with acting. She gave up tennis to pursue her career, though she decided to keep on riding, which was a choice she never regretted. "I have six horses, and they have been the biggest blessing in my life. Horseback riding is why I’m so centred [sic], especially in this business," she told The New Zealand Herald. "I wouldn’t have my career without it."

The next decade brought even more opportunities. Cuoco played Maureen McCormick in the TV movie "Growing Up Brady" in 2000. The same year, she scored a recurring role on the CBS sitcom "Ladies Man." Cuoco came on as Bonnie Stiles for Season 2, joining a cast that included Alfred Molina, Betty White, and Sharon Lawrence.

She was working nonstop and proving herself as an actress. But she still hadn’t gotten her big break.

8 Simple Rules changed Cuoco’s life

Kaley Cuoco had such a bad audition when she was a teenager that she almost blew her career. But producers could see she was right for the show and called her agent, asking if she would try again. In 2002, at age 17, she got her breakout role when she was cast as Bridget Erin "Beach" Hennessy on ABC’s "8 Simple Rules," starring John Ritter and Katey Sagal. As Bridget, Cuoco played the oldest child in the Hennessy family, a beautiful, ditzy blond preoccupied with boy drama. She embraced the role.

"So I did end up getting the job, which totally changed the course, truly, of, actually, my life and my career," she told Sidewalks. "It kind of put me on the map and made me realize how much I love sitcom."

When Ritter died suddenly in 2003, Cuoco was heartbroken, and the show faced an unexpected challenge. New characters were introduced and portrayed by actors including David Spade, James Garner, and Suzanne Pleshette. "8 Simple Rules" continued until 2005, and Cuoco knew she would never forget her time there. "To this day if anyone asks me [about] John Ritter, I get this chill because I love him so much," she told Entertainment Tonight.

Cuoco ‘charmed’ in her next major role

In 2005, Kaley Cuoco was offered a role on The WB’s "Charmed" in its eighth season. Now known for her work on "8 Simple Rules," she didn’t have to audition, and producers didn’t even mind that she’d never watched the show (per South Coast Today).

She was initially nervous to come on as Billie Jenkins, a new witch among a star-studded cast including Holly Marie Combs, Alyssa Milano, Rose McGowan, and Shannen Doherty. But she felt at home after a warm welcome from Milano. "I know what it’s like when someone new comes on," Cuoco told Yahoo Entertainment. "There’s people like [Alyssa] who really do mold your career and mold your path. So that was a really good moment."

Cuoco appeared in 22 episodes throughout the final season, and viewers hoped she might get a spin-off series. That was not to be, but fans would see her again onscreen soon enough.

Her Big Bang audition set off a whirlwind

When Kaley Cuoco first auditioned for "The Big Bang Theory," she didn’t get the part of Penny. In fact, the role didn’t even exist early on. Cuoco tried out for a different version of the character, a girl named Katie. At 19 years old, however, she was too young for the part. After filming the first pilot, producers decided to make some changes. That’s when they created Penny, brought Cuoco back, and cast her.

"I came in, I got the job and it got picked up and it was, like, this whirlwind," she told Entertainment Tonight. "It was awesome."

Penny started off as a bubbly, pretty, girl-next-door type. Over the course of 12 seasons on the show, Cuoco had the chance to put her skills to work, and she ran with it. She created an edgier character with more depth, who played a major role in the sitcom’s success. But the credit really goes to Cuoco herself, an actor who fans will follow to any future project.