One of the unspoken rules about every adult animated series is that the show will inevitably develop a sizeable roster of supporting characters that will often rival the core cast in popularity. With almost 30 years under its belt, South Park has conjured so many hilarious recurring characters that the series could fully transition away from Stan, Cartman, Kyle, and Kenny and suffer no ill effects. Hell, some could even argue that Randy Marsh's recent ascension in the series' hierarchy is an example of South Park doing just that.
Even though South Park's cast is immense and memorable, The Simpsons did it first. Over the course of its illustrious run, The Simpsons have produced so many iconic characters that entire television tropes have been named after them. In the video linked above, the YouTube channel Teemu_V created an hour-long compilation of the first appearances of several classic characters from The Simpsons.