Mary Cooper is the mother of Sheldon, his twin sister Missy and brother George Jr., and the widow of George Sr. Mary Cooper is played by Laurie Metcalf.
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 as a grown man, Mary still takes good 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 visits 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.
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.