A devout Christian woman, Mary lives in East Texas and works for the local church. On her visits to Pasadena, she has been shown to still be very mothering towards Sheldon, although they have a stark difference of opinion on matters of religion and science. Mary is proud of Sheldon's work even if she doesn't understand it all.
Even though he's a grown man, Mary still takes gentle care of Sheldon, including singing him Soft Kitty when he's sick. At times, though, her patience with Sheldon can snap. Mary has said "I love the boy to death, but he has been difficult since he fell out of me at the K-Mart." When Mary comes to town, she has also been shown to be motherly to Sheldon's friends.
Although she's usually a sweet, polite woman, Mary's views may be considered politically incorrect. Sheldon has described his mother as a "kind, loving, religiously fanatical, right-wing Texan, with a slightly out of scale head and a mild Dr. Pepper addiction".
Mary's husband and father to her children, George Cooper Sr., died during Sheldon's childhood. He has been described as an alcoholic who would often argue with his wife.
Mary had two other children with George, a twin sister for Sheldon, Missy, and an older brother, George Jr. Mary has described her two other children as "dumb as soup." Mary ensured Sheldon was there for Missy when she gave birth to a child at home, but it's suggested Mary does not have a close relationship with George. Jr, who she describes as an "idiot" who's dating a "whore".
Since her husband's death, Mary has been shown to have been open to dating again. When she visited Pasadena to get Sheldon his job back, she responded to flirtations from Sheldon's boss, Dr. Gablehauser. Later, Sheldon observed his mother having coitus with another man, who she later admitted she'd been dating for a few months. When Mary met Leonard's father, Alfred, they both enjoyed enjoy eachother's company and left the restaurant together, leading Sheldon and Leonard to fear they were spending the night together. Mary and Alfred later said they only shared a conversation, but that they might wish to meet up again later.
In The Luminous Fish Effect, Mary visited Pasadena after Leonard called her to say Sheldon had lost his job and taken up bizarre hobbies. Mary tried to slowly coax Sheldon out of his rut, but eventually she forced him to go to the University and apologize to his boss. While there, Mary and Dr. Gablehauser struck up a rapport, causing Sheldon to wonder whether Dr. Gablehauser was going to be his new daddy.
In The Panty Pinata Polarization, Leonard gave Mary's phone number to Penny, to end their tit-for-tat war, describing it as Sheldon's kryptonite. On the phone, Mary forces Sheldon to apologize to Penny.
In The Electric Can Opener Fluctuation, Sheldon returned home to Texas when he was embarrassed at the university after bragging about scientific results which the guys had altered to keep Sheldon happy. While back in Texas, Sheldon enjoyed the home comforts but his tolerance ran out when Mary insisted that evolution is just an opinion. Sheldon returned home with Leonard, Raj and Howard who had gone to bring him back.
Mary was once again called in by Leonard to help Sheldon in The Zazzy Substitution, when Sheldon responded badly to the termination of his relationship with his "girl who was a friend", Amy. Sheldon tried to replace Amy by adopting 25 cats. Mary was able to get Sheldon and Amy back together by saying they weren't suited for each other, and saying she would have had to end the relationship if they weren't already broken up.
In The Rhinitis Revelation, Mary's trip to Pasadena led to a rift with Sheldon when he wanted her to spend her time taking care of him and going to physics lectures, rather than going sight-seeing in Los Angeles with the rest of the gang. After Mary spent the day with his friends instead of him, Sheldon caught a cold and eventually got the maternal care he'd been hoping for.
In The Maternal Combustion, Mary visited Pasadena when Sheldon and Leonard's work was set to be honored. Her first time meeting Leonard's mother, Dr. Beverly Hofstadter, led to a clash over their religious views and their diametrically opposed parenting styles. After Sheldon talked to Beverly, and Mary talked to Leonard and Penny, the mothers were able to patch things up. In The Matrimonial Momentum, it was revealed that Mary was the person who gave Sheldon an engagement ring that he had planned to give to Amy before they split up.
In The Convergence Convergence, Mary visited Pasadena to attend Leonard and Penny's do-over wedding ceremony, after being invited by Sheldon. Mary and Beverly Hofstadter butted heads again over their different views on religion. When Mary met Alfred Hofstadter, Beverly's ex-husband and Leonard's father, they bonded over their mutual dislike of Beverly. After a meal the night before Leonard and Penny's second ceremony, Alfred and Mary excused themselves to go back to their hotel, leading Sheldon and Leonard to wonder whether their parents were hooking up.
In The Conjugal Conjecture, Sheldon confronted Alfred to ask what he and his mother had been doing after they left the restaurant. Alfred said they only shared a cab and conversation. Later, Alfred admitted that they had decided that Mary might come to New York to visit him.
In The Holiday Summation, Sheldon and Amy visited Mary over the holidays to tell them that they were now living together. Sheldon expected that his mother would disapprove of their living situation because of her religious beliefs, but Mary said she was very happy for Sheldon given his "special circumstances" even if she would prefer they weren't living out of wedlock. Sheldon was offended that his mother assumed he would be alone for the rest of his life. Upset with his mother, Sheldon started to act out and then left the house with Amy, who finally admitted she had already told Mary they were living together.
In The Proposal Proposal, Sheldon phoned Mary to tell her that he and Amy were engaged. Mary was happy for Sheldon but she was not surprised as she had been praying for them. Sheldon informed his mother that they would not be getting married in a church, which was okay with Mary as she said anywhere Jesus is is a church and he'll be there in her heart.
In The Solo Oscillation, Sheldon was annoyed when his important work was interrupted by a phone call from Mary to say she had run into somebody he used to know, Mr. Watkins. Sheldon started to obsess over the details and eventually worked out the odds of Mary running into him. When Sheldon called his mother back to tell her the answer was 1 in 18 million, Mary informed him that Mr. Watkins had passed away that morning. When she remarked "What are the odds of that?", Sheldon said he would call her back.
- According to Sheldon, Mary has a mild addiction to the soft drink Dr. Pepper.
- Mary told Alfred Hofstadter that she works at her local church.