The very first pilot of "The Big Bang Theory," starring Amanda Walsh playing Katie, and a female friend called Gilda played by Iris Bahr.

Celebrating the 100th episode of US sitcom "The Big Bang Theory," Rick Edwards travels to the Hollywood set for an access-all-areas visit, catching up with the cast and learning everything there is to know about the show. This behind-the-scenes special takes fans through everything from the writing of the script to the recording of the show in front of a live audience.

As "The Big Bang Theory" celebrates its 100th episode, Rick Edwards looks back at some of the US sitcom's most hilarious and memorable scenes and talks with the cast and crew on the set in Hollywood. The actors share their favorite moments and reveal a few secrets about the making of the show.

The cast and crew of "The Big Bang Theory" answer questions from the fans at Comic-Con 2015.

The writers of "The Big Bang Theory" answer questions during the 2016 Comic Con Writers Panel.

Johnny Galecki and Kaley Cuoco lead fans on a trip down memory lane, sharing some of the best-kept backstage secrets and personal memories from the past 12 years. They reveal their favorite moments playing beloved characters Leonard and Penny, and revisit some of the most memorable stories from “The Big Bang Theory Stage.” Additionally they tour the iconic sets, including Leonard and Sheldon’s apartment and show unforgettable clips and interviews to celebrate this beloved series.