The Big Bang Theory has become one of the most successful sitcoms of all time since it first aired back in 2007.

Would it really be the same without Kaley Cuoco though?

Her character Penny has featured from the start, the wannabe actress is just as important to the show as the four nerds who hang out across the hall.

And she's the inspiration behind Sheldon's hilariously annoying door knocking routine...


While Cuoco may be a star name now, up until then her role in '8 Simple Rules' had been her biggest and she very nearly missed out on the Big Bang.

The original lead was called Katie and Amanda Walsh was cast in the role.

Walsh even appeared in an unaired pilot for the show.

Cuoco told Vegas Magazine that it took her three attempts to win the part, so much like Penny she never gave up on her dream of landing a big role.


She's come a long way since then, earning $1 million per-episode along with co-stars Jim Parsons and Johnny Galecki.

No offence to Walsh, but it just wouldn't have been the same without Penny...