For sheer volume, "Gunsmoke" was the longest-running television series, according to HowStuffWorks. From 1955 to 1975, CBS aired 635 episodes. The show centered on the marshal in Dodge City, Kan., during the Wild West period. The series began as a radio show in 1952.
Although it has not produced as many episodes as "Gunsmoke," "The Simpsons" has been on television for more years. It began in 1989, and, as of 2014, is still on the air. This animated show follows the antics of the title characters, which include parents, a smart-aleck son, a clever daughter and a baby girl. The show has a reputation for having celebrities play cartoon versions of themselves.