The series finale of "The Big Bang Theory" airs on Thursday, concluding the longest-running multicamera series of all time.

After 12 seasons, the sitcom was still one of the most popular shows on TV. It was the second-highest-rated series of 2018 according to Nielsen ratings, only behind "Roseanne."

And both of those shows were canceled.

Actor Jim Parsons decided not to renew his contract last year, putting the final nail in the show's coffin and walking away from $1 million an episode. The final season premiered in September.

READ MORE : The 30 most popular shows from Netflix and other streaming services in 2019, so far

"It was the first time in my life of doing this show that it occurred to me that I might want tonotdo another contract after [season] 12 was up," Parsons told The Hollywood Reporter ."I don't know if it's because I'm an Aries or just because maybe I'm in touch with myself. Whatever it is, once I had that thought, I was like, 'Well, that's your answer.'"

The "Big Bang Theory" universe isn't dead, though. "Sheldon," a prequel series, was among the most popular shows last years, as well.

"Roseanne" held tight the entire year as the biggest show of 2018 after it premiered in March. The revival was quickly canceled after one season after the show's star Roseanne Barr tweeted a racist remark at former Obama adviser Valerie Jarrett. It was replaced with a spin-off named "The Conners," which premiered in October to lower, but not bad, ratings .

Below are the nine biggest shows of 2018, according to Nielsen ratings:

9. "Bull" CBS

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CBS

Average viewers: 13.5 million

Summary: "Stars Michael Weatherly as Dr. Jason Bull in a drama inspired by the early career of Dr. Phil McGraw, the founder of one of the most prolific trial consulting firms of all time."

8. "America's Got Talent" (Tuesdays) NBC

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NBC

Average viewers: 14.3 million

Summary: "The all-new winter edition of TVs No. 1 alternative series, "America's Got Talent: The Champions," premieres Monday, January 7 at 8/7c.

The series, from NBC,Fremantle and Syco Entertainment, will feature the star-studded judges panel from "America's Got Talent" - Executive Producer Simon Cowell, Mel B, Heidi Klum and Howie Mandel - as well as Host Terry Crews, co-star of NBCs "Brooklyn Nine-Nine."

7. "The Good Doctor" ABC

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ABC

Average viewers: 14.5 million

Summary: "Freddie Highmore plays Shaun Murphy, a young surgeon with autism and savant syndrome, relocates from a quiet country life to join a prestigious hospital's surgical unit."

6. "Manifest" NBC

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NBC

Average viewers: 14.6 million

"When Montego Air Flight 828 landed safely after a turbulent but routine flight, the crew and passengers were relieved. Yet in the span of those few hours, the world had aged five years and their friends, families and colleagues, after mourning their loss, had given up hope and moved on. Now, faced with the impossible, they're all given a second chance."

5. "Young Sheldon" CBS

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Average viewers: 15.7 million

Summary: "Follows the 9-year-old Sheldon Cooper as he navigates living with his family in East Texas and going to high school."

4. "This Is Us" NBC

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NBC

Average viewers: 16.6 million

Summary: "Everyone has a family. And every family has a story. 'This Is Us' chronicles the Pearson family across the decades."

3. "NCIS" CBS

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CBS/Bill Inoshita

Average viewers: 16.7 million

Summary: "'NCIS' (Naval Criminal Investigative Service) is more than just an action drama. With liberal doses of humor, it's a show that focuses on the sometimes complex and always amusing dynamics of a team forced to work together in high-stress situations."

2. "The Big Bang Theory" CBS

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CBS

Average viewers: 18.3 million

"Leonard and Sheldon are brilliant physicists geniuses in the laboratory but socially challenged everywhere else. Enter beautiful, street-smart neighbor Penny, who aims to teach them a thing or two about life."

1. "Roseanne" ABC

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ABC

Average viewers: 20 million

Summary: "Explore life, death and everything in between through the relatable, hilarious and brutally honest lens of the Conner household."

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