The Big Bang Theory premiered in the United States on September 24, 2007 on CBS. The series debuted in Canada on CTV in September 2007.[152] On February 14, 2008, the series debuted in the United Kingdom on channels E4 and Channel 4.[153] In Australia the first seven seasons of the series began airing on the Seven Network and 7mate from October 2015 and also gained the rights to season 8 in 2016, though the Nine Network has rights to air seasons nine & ten.[154][155] On January 22, 2018, it was announced that Nine had acquired the rights to Season 1–8.[156]
In March 2017, CBS renewed the series for two additional seasons, bringing its total to twelve, and running through the 2018–19 television season.[3] On August 22, 2018, CBS and Warner Bros. Television officially announced that the twelfth season would be the series' last. This stems from Jim Parsons' decision to leave the series at the end of the season if the show were to have been renewed for a thirteenth season.[1][4][5] The series concluded with an hour-long finale consisting of two back-to-back episodes on May 16, 2019.[6][7] A retrospective, hosted by Johnny Galecki and Kaley Cuoco, aired at 9:30 P.M. ET/PT, the night of the finale, following the season two finale of Young Sheldon.[8]
^ "Editor's Note: With final Monday ratings in, The Big Bang Theory has now reached a new series high in viewers (16.32m) and was the night's top program in adults 18-49 (5.9/15), up a tenth from this morning. -- "Two and a Half Men" Soars to Its Best Adult 18-49 Rating in Three Years". CBS. March 9, 2010. Archived from the original on January 8, 2014. Retrieved January 5, 2013.

Sara Gilbert as Leslie Winkle (recurring season 1, starring season 2, guest seasons 3, 9):[47][48][49] A physicist who works in the same lab as Leonard. In appearance, she is essentially Leonard's female counterpart and has conflicting scientific theories with Sheldon. Leslie has casual sex with Leonard and later Howard. Gilbert was promoted to a main cast member during the second season but resumed guest star status because producers could not come up with enough material for the character.[47] Gilbert returned to The Big Bang Theory for its 200th episode.[50]
Penny runs into her ex-boyfriend Zack, who has gotten rich from selling his company and married a similarly dim-witted woman named Marissa. Meeting with Leonard and Penny, they say Zack is infertile and ask to pay Leonard as a sperm donor so they can have a baby. Leonard is flattered, but Penny finds it creepy. Leonard says that since Penny decided she did not want to have children, he should be allowed to help another couple with this issue. Sheldon advises him to think about the emotional toll this could have on him. Leonard says he will not do it if Penny objects; Penny says she will support whatever decision Leonard makes. Meanwhile, Raj tries to get Anu back but she points out he just wanted to be married like his friends. Raj points out that Anu is similarly looking for a quick marriage. He admits to Anu that he really likes her and they decide to start their relationship as just dating.
By season seven, Galecki, Parsons, and Cuoco were also receiving 0.25% of the series' back-end money. Before production began on the eighth season, the three plus Helberg and Nayyar, looked to renegotiate new contracts, with Galecki, Parsons, and Cuoco seeking around $1 million per episode, as well as more back-end money.[36] Contracts were signed in the beginning of August 2014, giving the three principal actors an estimated $1 million per episode for three years, with the possibility to extend for a fourth year. The deals also include larger pieces of the show, signing bonuses, production deals, and advances towards the back-end.[37] Helberg and Nayyar were also able to renegotiate their contracts, giving them a per-episode pay in the "mid-six-figure range", up from around $100,000 per episode they each received in years prior. The duo, who were looking to have salary parity with Parsons, Galecki, and Cuoco, signed their contracts after the studio and producers threatened to write the characters out of the series if a deal could not be reached before the start of production on season eight.[38] By season 10, Helberg and Nayyar reached the $1 million per episode parity with Parsons, Galecki, and Cuoco, due to a clause in their deals signed in 2014.[39]
After Sheldon reminds the guys about the time they mined Bitcoin without him, the guys go on a quest to find their suddenly valuable missing cryptocurrency. They realize the currency is on a laptop which Leonard gave to Penny when they dating, which she then gave to her ex-boyfriend Zack. After Leonard and Penny go to Zack's apartment, he shows them a seven-year-old video that Penny recorded on the laptop soon after she broke up with Leonard. Leonard is touched by the video which shows a drunk Penny lamenting the break-up of her relationship with him.
Warner Bros. Television controls the online rights for the show.[159][160] Full episodes are available at tv.com, while short clips and recently aired full episodes are available on cbs.com.[161] In Canada, recent episode(s) and pictures are available on CTV.ca.[162] Additionally in Canada, the first six seasons are available for streaming on Bell Media's CraveTV.[163] After the show has aired in New Zealand the shows are available in full online at TVNZ's on demand web service.
After Sheldon has a food truck moved away from the building, Leonard and Penny are shocked to find he is the leader and sole member of the Tenants' Association for the building. Amy doesn't want to be caught in the middle but secretly suggests they rally support from the other tenants to vote Sheldon out. Nobody else supports Leonard so Amy tells them Sheldon was never added to the lease when he moved across the hall with her. Sheldon fires back with his own legal technicality so Amy is forced to support Leonard. She makes Sheldon happy by saying he can be Leonard's official opposition, making Leonard believe he made a mistake. Meanwhile, Howard and Raj find a drone. Raj returns it to the cute owner Cynthia and gets her number. Unfortunately, Cynthia watches footage of Raj on the drone and is immediately turned off.

Two physicists from Chicago, Dr. Campbell and Dr. Pemberton, accidentally prove Sheldon and Amy's super-asymmetry theory. This puts them on track for a Nobel Prize, but Leonard points out they tend to go to the experimental scientists who prove a concept instead of theorists like Sheldon who come up with it. Meeting with them, they tell Sheldon they are willing to share the Prize but only three names can be on the submission, and they want to cut Amy out. Amy does not want to prevent Sheldon's lifelong dream, but he goes to President Seibert who agrees to fight for Amy on their behalf. Meanwhile, Bernadette's drug has been approved and she wants to promote Penny to lead the marketing team. Penny resists, knowing Bernadette's attitude at work and doubting her own inexperience to take the responsibility, but Bernadette uses reverse-psychology to get Penny to take the job. Penny mirrors Bernadette's commanding style to get the other employees in line, impressing Bernadette.
Kunal Nayyar as Rajesh Koothrappali:[46] A particle astrophysicist originally from New Delhi, India. Raj is initially unable to talk to women unless he drinks alcohol. Raj also has very feminine tastes and often takes on a stereotypical female role in his friendship with Howard as well as in the group of four men. Raj later dates Lucy (Kate Micucci), who also suffers from social anxiety, but it eventually ends; he later speaks to Penny without alcohol and thus overcomes his selective mutism. He begins dating Emily and their relationship later becomes exclusive. Raj also has a Yorkshire Terrier named Cinnamon.

The Canadian alternative rock band Barenaked Ladies wrote and recorded the show's theme song, which describes the history and formation of the universe and the Earth. Co-lead singer Ed Robertson was asked by Lorre and Prady to write a theme song for the show after the producers attended one of the band's concerts in Los Angeles. By coincidence, Robertson had recently read Simon Singh's book Big Bang,[25][26] and at the concert improvised a freestyle rap about the origins of the universe.[citation needed] Lorre and Prady phoned him shortly thereafter and asked him to write the theme song. Having been asked to write songs for other films and shows, but ending up being rejected because producers favored songs by other artists, Robertson agreed to write the theme only after learning that Lorre and Prady had not asked anyone else.[citation needed]
Johnny Galecki as Leonard Hofstadter:[42] An experimental physicist with an IQ of 173, who received his PhD when he was 24 years old. Leonard is a nerd who loves video games, comic books, and Dungeons & Dragons. Leonard is the straight man of the series, in which he shares an apartment in Pasadena, CA, with Sheldon. Leonard is smitten with his new neighbor Penny when they first meet, and they eventually marry.
Melissa Rauch as Bernadette Rostenkowski-Wolowitz (recurring season 3, starring seasons 4–12):[51] A young woman who initially is a co-worker at The Cheesecake Factory with Penny to pay her way through graduate school, where she is studying microbiology. Bernadette is introduced to Howard by Penny; at first, they do not get along, apparently having nothing in common. They date and later get engaged and married. Although generally a sweet and good-natured person, Bernadette has a short fuse and can be vindictive and lash out when provoked.
Sheldon and Amy's wedding day arrives, with many friends and family attending, including Amy's domineering mother (Kathy Bates) and quiet father (Teller); Sheldon's mother Mary, brother George, and sister Missy, who is pregnant with her second child and separated from her husband; and Mark Hamill, who replaces Wil Wheaton as officiant as a favor to Howard who returned his lost dog. Sheldon cannot get his bow-tie to be symmetrical and conversations with Amy and his mother give him an epiphany about superasymmetry. Sheldon and Amy, along with Leonard, get caught up figuring out the math of the theory during the wedding ceremony, making Hamill take Star Wars questions to stall for time. Penny retrieves the couple, who then decide that they have the rest of their lives to make science together. Amy and Sheldon then express their vows. Amy recites a set of heartfelt vows, leaving Sheldon initially at a loss for words, before he reciprocates her loving words. They are pronounced as husband and wife.
Two physicists from Chicago, Dr. Campbell and Dr. Pemberton, accidentally prove Sheldon and Amy's super-asymmetry theory. This puts them on track for a Nobel Prize, but Leonard points out they tend to go to the experimental scientists who prove a concept instead of theorists like Sheldon who come up with it. Meeting with them, they tell Sheldon they are willing to share the Prize but only three names can be on the submission, and they want to cut Amy out. Amy does not want to prevent Sheldon's lifelong dream, but he goes to President Seibert who agrees to fight for Amy on their behalf. Meanwhile, Bernadette's drug has been approved and she wants to promote Penny to lead the marketing team. Penny resists, knowing Bernadette's attitude at work and doubting her own inexperience to take the responsibility, but Bernadette uses reverse-psychology to get Penny to take the job. Penny mirrors Bernadette's commanding style to get the other employees in line, impressing Bernadette.
Initial reception for the series was mixed. The review aggregation website Rotten Tomatoes reported a 52% approval rating for the first season based on reviews from 23 critics, with an average rating of 5.18/10. The website's critical consensus reads, "The Big Bang Theory brings a new class of character to mainstream television, but much of the comedy feels formulaic and stiff."[91] On Metacritic, the season holds a score of 57 out of 100, based on reviews from 23 critics, indicating "mixed or average reviews".[92] Later seasons received more acclaim and in 2013, TV Guide ranked the series #52 on its list of the 60 Best Series of All Time.[93] 

Leonard's mother Beverly visits, and he is thrilled when she takes an interest in his work. However, when he learns that she is doing research on him for a new parenting book, he is furious. He prepares to tell her how she let him down over the years, but instead chooses to accept and forgive her, and forgive himself for holding onto that resentment for so long. Beverley is touched that he forgave her and they share a genuine hug. Meanwhile, Anu gets a job offer in London. Raj prepares to fly out and propose to her, ready to follow her if she accepts. Howard stops Raj at the airport, saying there is a better match out there for him, convincing Raj to return home. Stuart and Denise are bothered by her creepy roommate Mitch, while Bernadette and Howard are tired of Denise constantly staying overnight with Stuart at their house. Stuart says he is ready to move in with Denise, and they say they love each other while convincing Mitch to move out.

They are also fans of Star Wars, Battlestar Galactica, and Doctor Who. In the episode "The Ornithophobia Diffusion", when there is a delay in watching Star Wars on Blu-ray, Howard complains, "If we don't start soon, George Lucas is going to change it again" (referring to Lucas' controversial alterations to the films) and in "The Hot Troll Deviation", Katee Sackhoff of Battlestar Galactica appeared as Howard's fantasy dream girl. The characters have different tastes in franchises with Sheldon praising Firefly but disapproving of Leonard's enjoyment of Babylon 5.[76][n 1] With regard to fantasy, the four make frequent references to The Lord of the Rings and Harry Potter novels and movies. Additionally, Howard can speak Sindarin, one of the two Elvish languages from The Lord of the Rings.


The Canadian alternative rock band Barenaked Ladies wrote and recorded the show's theme song, which describes the history and formation of the universe and the Earth. Co-lead singer Ed Robertson was asked by Lorre and Prady to write a theme song for the show after the producers attended one of the band's concerts in Los Angeles. By coincidence, Robertson had recently read Simon Singh's book Big Bang,[25][26] and at the concert improvised a freestyle rap about the origins of the universe.[citation needed] Lorre and Prady phoned him shortly thereafter and asked him to write the theme song. Having been asked to write songs for other films and shows, but ending up being rejected because producers favored songs by other artists, Robertson agreed to write the theme only after learning that Lorre and Prady had not asked anyone else.[citation needed]
When Raj misses out on a job at the planetarium, his father says he has no confidence because Howard always makes fun of him. Raj distances himself from Howard and later gets the job. Howard is hurt by this (even after apologizing to him) and tries to make amends with Raj after his first performance at the planetarium but, when he sees him get a date, he leaves without speaking to him, thinking that the latter's life is better without him. Meanwhile, Sheldon and Amy try randomly dividing up wedding tasks, but they keep arguing. The only thing they can agree on is to get married, so they decide to just get married at City Hall. However, Sheldon decides that he wants a first dance with his new wife and they go home to plan their wedding. 
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