In the final scene of the 1979–1980 season, the character J. R. Ewing, played by Larry Hagman, was shot by an unknown individual. The episode, titled "A House Divided", was broadcast on March 21, 1980. Viewers had to wait all summer, and most of the autumn because of a Hollywood actors' strike (and Hagman's own holdout), to learn whether J.R. would survive, and which of his many enemies was responsible.
T-shirts printed with such references as "Who Shot J.R.?" and "I Shot J.R." became common over the summer. Betting parlors worldwide took bets as to which one of the 10 or so principal characters had actually pulled the trigger. A session of the Turkish parliament was suspended to allow legislators a chance to get home in time to view the Dallas episode.
During the presidential campaign of 1980 (which led to the election of Ronald Reagan), the Republicans edited an official badge saying "A Democrat shot J.R.", which influenced the polls according to some sources. Jimmy Carter claimed that he would have had no problem financing his campaign if he had known who shot J.R.
Viewers had to wait an additional two months to find out the answer to the famous question, as a strike by the Screen Actors' Guild in July, 1980 caused the production of most new network shows to be delayed by eight weeks. Ultimately, the person who pulled the trigger was revealed to be Kristin Shepard (played by Mary Crosby) in the "Who Done It?" episode which aired on November 21, 1980. Kristin was J.R.'s scheming sister-in-law and mistress, who shot him in a fit of anger. J.R. didn't press charges, as Kristin claimed she was pregnant with his child as a result of their affair.
It was, at the time, the highest rated television episode in US history. It had a Nielsen rating of 53.3 and a 76% share, and it was estimated that 83,000,000 people watched the episode. The previous record for a TV episode, not counting the final installment of the miniseries Roots, had been the 1967 finale for The Fugitive. "Who Shot J.R.?" now sits third on the list, beaten in 1983 by the final episode of M*A*S*H and Super Bowl XLIV but still remains the highest rated non-finale episode of a TV series by a wide margin.
The great success of this 1980 stunt helped popularize in the US the practice of ending a television season with a cliffhanger. The episode also inspired a novelty record by radio personality Gary Burbank, which hit the Billboard Top 100 in 1980.