Spin-off from the sketch comedy series The Tracey Ullman Show, which featured animated Simpsons sketches. These proved popular enough to spawn a Simpsons Christmas special, which served as the pilot for the series. As of 2015 it is the longest continually-running scripted prime time series with ongoing characters and longest continually-running animated series in US TV history, and if its occasional fantasy interludes are taken into account, it is also the longest-running fantasy-style series on English-language television.
Currently the longest-running scripted American series of all time, at last report renewed until at least its 28th season. Amazingly it wasn't until this past month (May 2015) that it lost its first major voice actor, Harry Shearer (who plays far more characters than just Ned Flanders). By comparison, the original Doctor Who ran for only 26 years, and the longest-running live-action American scripted series were Gunsmoke and Law & Order, both of which survived for 20 seasons. I know there's been a lot of hate for The Simpsons, with many feeling its best days were back in the 90s, but you have to respect the longevity. The world seriously will not feel the same when the show finally ends.