"The Simpsons" will celebrate a milestone on Sunday. After airing its 636th episode, the animated show will become the longest-running primetime scripted series, surpassing CBS' "Gunsmoke," which aired 635 episodes from 1955 to 1975.
The show is in its 29th season and began in 1989. In last week's episode, Homer mentioned that their show was about to surpass "Gunsmoke," when Bart pointed out that the Western show also had radio episodes.
In the upcoming episode's opener, Maggie helps Springfield beat Dodge City in a duel against Marshal Matt Dillon. The episode, titled "Forgive and Regret," will focus on Grampa Simpson, who becomes deathly ill and makes a confession.