Alex is pursuing her Ph.D. in Caltech Physics and works as Sheldon’s assistant. Sheldon often gives her tasks that are unrelated to their research.
Alex wants Leonard and asks him on a date, but Leonard says no because of his loyalty to Penny.
Sara Rue as Stephanie Barnett – Then
Stephanie works as a doctor and highly distinguished surgical resident at Fremont Memorial Hospital. She is introduced in season 2 when Howard tries to seduce her and allows her to drive a Mars Rover.
Instead, Stephanie meets and falls for Leonard, and the pair ends up dating. Stephanie moves all of her belongings into Leonard’s apartment, and Leonard soon ends their relationship through a text message.
Sara Rue as Stephanie Barnett – Now
Sara has been cast in multiple TV shows since her role as Stephanie. She played Kim Sallinger in "Malibu Country," Brenda in "Rules of Engagement," and Candace in "Mom."
She's also had regular roles in the TV shows "A Series of Unfortunate Events," "American Housewife," and "B Positive."
Margo Harshman as Alex Jensen – Now
Margo’s acting career didn’t start in TBBT, rather back when she was a kid in "Even Stevens," playing the role of Tawny Dean, the best friend of was Shia LaBeouf’s character, Louis Stevens.
Margo has played several smaller parts since TBBT, like Alison Kidman in "Bones" and Delilah Fielding in "NCIS."
Brian Patrick Wade as Kurt – Then
Kurt plays the role of Penny’s former boyfriend. The two lived together after Penny moved from Nebraska to California.
Kurt, unlike the guys, isn’t very bright, but he’s a tall, muscular, and formidable guy. Kurt and Leonard naturally have some beef, and it takes Penny some time to get over Kurt, although she finds him to be a jerk.