Bernadette is a former waitress at The Cheesecake Factory who has finished her Ph.D. in microbiology. She was introduced to us in the third season when Penny introduced her to Howard.
At first, the two weren’t able to find anything in common but then bonded over the fact that they both have overbearing mothers. In season 4, Howard proposes to her, and they get married in season 6. Later, the two have two kids — a daughter named Halley and a son named Neil.
Kaley Cuoco as Penny Hofstadter – Then
Penny is Sheldon and Leonard’s beautiful blonde neighbor who is introduced in the first season. She considers herself a professional actress, although her acting resume is very short.
Penny gets most of her money from waitressing at The Cheesecake Factory. She has been Leonard’s love interest since the first episode and the couple dated on and off throughout the seasons until they eventually got married in Vegas in season 9. She later took a break from being an actress and started to work at Bernadette’s pharmaceutical company instead.
Kaley Cuoco as Penny Hofstadter – Now
Kaley Cuoco had a major role in a sitcom before TBBT. Before starring as Penny, Kaley played the lead role of Bridget Hennessy in the sitcom "8 Simple Rules," co-starring with the late John Ritter.
Kaley, along with her costars Jim and John, is one of TV’s highest-paid comedy actors and made $900,000 per episode for her role as Penny. The actress has become a millionaire from her television work and went on to launch her own production company.
Melissa Rauch as Bernadette Wolowitz – Now
Before her major role in TBBT, Melissa made some other television appearances. She played minor parts in "The Office" and "True Blood."
Melissa also acted in a few movies such as "The Bronze" in 2015 and "Are You Here" in 2013. The actress (along with Mayim) got a raise after she signed on for season 11 and 12 and started making a whopping $500,000 per episode.
Bob Newhart as Arthur Jeffries — Then
Arthur Jeffries was the host of the kids' science show, "Professor Proton." Sheldon and Leonard looked up to him as kids, and they later become involved with him in real life, much to their delight.
In season seven, Jeffries dies, but that doesn't mean he was off the show. He kept coming up for a few more appearances in Sheldon's dreams, usually looking a little disoriented and wearing a "Star Wars" costume.