THE SIMPSONS (FOX)
Scheduling history: The vast majority of The Simpsons' run has come on Sunday. The show was on Sunday in its short first season all the way back in early 1990, then moved to Thursday for the next four years, then went back to Sunday for fall of 1994 and has been on that evening for the over two decades since.
See (who saw) how it all began: Like other posts for Law & Order and ER, The Simpsons is a show for which I'm unfortunately missing a ton of information. As with those two shows, I start tracking in 1999-00, the first year in which I have any reasonable amount of data. But I did see some numbers on the series premiere on 1/14/90. I saw a couple conflicting reports, so this really should be taken with a pretty massive grain of salt, but the number I'm going with is 24.53 million viewers and a 12.4/26 demo. I also saw a higher demo number that could be right. (I went with the lower one since it seemed to match the number of viewers better.) Either way, the premiere was one of the biggest in Fox history.
The best of times: Unlike ER and L&O, which seemingly peaked around the time I started getting data, I don't really know for sure on The Simpsons, so all I can really say is that the best seasons of data I have were from that period, circa 2000. The best regular in-timeslot data I have is the 9.9 and 10.4 demos scored by the one-hour show on 2/16/03 advertised as the 300th episode. (Though they were actually the 302nd and 303rd in broadcast order.)
The worst of times: The Simpsons has mostly gone downhill since then, though it's stayed close to even after accounting for the league average decline. Season 27 set a new series low with a 1.0 demo on 4/3/16.
Then vs. now: Of all the shows we've looked at (certainly all the big-four shows), The Simpsons is probably the most meaningful to the entire history of its network. Fox started in the 1986-87 season, so The Simpsons began in the fourth year of the net's nearly three decades of existence, and it's still going strong today. The mid-aughts were the last time the show took a year-to-year drop massively more than the league average. That's not bad at all over that long a period of time (though the NFL lead-ins have probably helped), and the show remains a really viable primetime player because it's still so strong in the younger male demos. Like Law & Order, it's proven that the key to longevity isn't necessarily staying at the very top of the primetime heap, as The Simpsons hasn't been close to those levels in many years. But thanks to its staying close to even, it should remain near the top in the numbers that matter most of all: ad dollars.
Adults 18-49 info by season:
Historical-adjusted ratings by season:
For more on The War of 18-49, my look at the history of primetime TV's veteran shows, see the Index.