18. Fred Flintstone
Since its debut on December 17, 1989, the Simpsons has broadcast 533 episodes throughout its 25 season-run. The Matt Groening animation is the longest-running American sitcom, the longest-running American animated program, and in 2009 surpassed 'Gunsmoke' as the longest-running American primetime, scripted television series. Before these successes, the previous most successful prime-time cartoon was Hanna-Barbera's The Flintstones, which was the most financially successful network animated franchise for three decades until Homer and his clan turned up. How fitting then that two of television's most famous of animated families should meet each other in a couch gag, which is exactly what happens in the 1992 season four opener, 'Kamp Krusty', when the Simpsons return home to find Fred, Wilma and Pebbles seated upon their sofa. This gag was poignantly repeated four years later for the 167th episode of the Simpsons, which officially broke The Flintstones' record of 166.