The decision by the creative minds behind The Simpsons to extend the reach of Springfield and focus on the everyday lives of a massive ensemble of colourful characters and caricatures was an ingenious one that allows the writers rich opportunity to explore new dynamics as the Simpsons family are able to interact with others. Had the show been limited to the smaller cast, we might not have seen the diversity needed to extend the show for such a long time, despite the accepted brilliance of the main cast. Naturally, as part of that ensemble, there are certain characters who stand out more than others, and who are given the greatest lines by writers who clearly love them more than their fellow players. They are the supporting stars who completely steal their scenes, grabbing all focus with a well-placed one-liner or their general, brilliant demeanour. The lack of screen time also allows these characters to be more brash, more annoying, and more grotesque, as absence dulls expectations of them and simultaneously heightens their impact every time we see them. They are the unheralded heroes of the show, pushed aside by the likes of more recurring supporting characters like Barney Gumble, Ned Flanders, Mr Burns, or the extended Simpsons family, but they deserve their time in the sun. These are not just the greatest supporting or recurring characters, nor are they necessarily the best developed, or even the best written, but they are the type of characters who appear, no matter how briefly, and completely steal focus from everyone else. They are memorable, whether for their irresistible soundbites, or the lunacy of their very condition, and we're paying tribute to the greatest of their number.
Honourable Mention
Cecil Underdunk Terwilliger
The stuffy and down-trodden younger brother of Sideshow Bob doesn't strictly qualify as a recurring supporting character, as he and his brother are both guest stars (and basically inflated cameos) but he is a brilliant character who added a new level to Bob's character, and who traded on the irresistible rapport that already existed between vocal stars Kelsey Grammer and David Hyde Pierce. His scheming is more devious and more Machiavellian even than his brother's - thanks to a lifetime of being over-looked in favour of Bob as the family star, and the complexities that underpin the character are devilishly well-written to the point where it feels a shame that we haven't had more screen time from the lesser Terwilliger brother.