Susan (last name unknown) is the mother of Penny and wife of Wyatt. She also has two other children, one boy named Randall and a second girl who we have never met. She lives with her husband outside of Omaha, Nebraska on their small farm where they raised their three children.
She was the only mother of any members of the gang who hadn't been seen on the show for quite a long time until she finally appeared in the first episode of Season 10/208th episode "The Conjugal Conjecture", except for Stuart Bloom's mother who up to that point is only mentioned and Emily Sweeney's mother and Leslie Winkle's mother who both haven't been seen or mentioned.
In "The Flaming Spittoon Acquisition", Sheldon implies that she's fat (as well as in "The Pulled Groin Extrapolation" where he states he has seen pictures of her and sarcastically encourages Penny to keep eating) and Penny reveals that her mother smoked pot when she was pregnant with her.
In "The Transporter Malfunction", Leonard and Sheldon told Penny they didn't want to open the Star Trek Transporters she had just bought them because once you open the box, it loses its value. Penny relied, "Yeah, yeah, my mom gave me the same lecture about my virginity. I gotta tell you, it was a lot more fun when I took it out and played with it."
In "The First Pitch Insufficiency", Amy wants to know when Penny and Leonard are getting married. They haven't set a date and Penny wants to wait long enough to prove to her mother that she's not pregnant.
In "The Bachelor Party Corrosion", Penny tells her father that she eloped with Leonard. Her mother was out with Penny's brother Randall who was celebrating being sober for one month and had received his 10th chip on account of being sober for a month. Her mother was going to make her son a little necklace to commemorate the occasion.
In "The Conjugal Conjecture" Susan first appears in person where she visits California with her son and husband to attend Leonard and Penny's wedding redo and is worried about her son that has formerly been on parole and what Leonard's parents would think about them.
Susan is a neurotic and stressed out woman, all from having had to deal with her troubled son. She was also seen to be whiny, including when someone tells her something good, like when Wyatt tried to make the trip happy, she told him to quit it.
Susan loves her daughter a lot, but it seems there has been a bit of tension between them.
Susan and Wyatt are obviously happily married and so they are a good couple. Although during Susan's first appearance, things are a bit tense between them about Randall's drug actions and his ending up in jail.
Susan's relationship with her other daughter, Penny's sister is not known but it's obvious she loves her very much.
Meanwhile, Susan's relationship with Penny's brother Randall is seen to be a bit tense since he has been ending up in and out of jail and Wyatt may not have been strict enough about that.
Like her husband, Susan is very fond of Leonard. She sees him as the first smart boyfriend Penny has dated and looked very proud at the wedding redo.
The rest of the gang
Susan never met any of Penny and Leonard's friends yet who are members of the gang until "The Conjugal Conjecture" where she was with them at Leonard and Penny's re-wedding, but didn't speak to anyone. However, during the ride to the airport, she said that they are just lovely, although Sheldon is a bit peculiar.
- Kaley Cuoco originally had stated that she would like to have Lisa Kudrow play Penny's mother; however, she was quite pleased working with her former character's mother from "8 Simple Rules".
- When Penny talks to her mother about being mother she tells her mother that she is not pregnant which was a first for their family.
- She had already met Leonard off-screen before her first appearance. This was hinted in "The Bachelor Party Corrosion" when Penny, Bernadette and Amy are discussing Penny waiting to tell her parents she got married to Leonard, Amy says "Well, it's kind of sad that they don't know. I mean, they love Leonard." referring to Wyatt and Susan. It has since been confirmed in her first appearance ("The Conjugal Conjecture").
- According to a July 2016 article on the TBBT Facebook page, actress Katey Sagal has been cast as Penny's mother, Susan, and will be seen in the Season 10 premiere. This will be a reunion of sorts for Sagal and Cuoco, who played mother and daughter on the sitcom 8 Simple Rules. Kaley has stated that Katey is her "TV mom".