Every Time The Simpsons Killed Characters (In Canon)

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The Simpsons has never taken continuity too seriously, but there are a handful of dead Simpsons characters that the show killed off for good. Over its many years onscreen, The Simpsons has inevitably racked up a few deaths, but the number of recurring characters killed off by the series remains relatively low. Characters like Dr. Nick and Dr. Marvin Monroe have been killed off only to rejoin the show, with future episodes ignoring their death. However, with the extensive ensemble of characters, there have been some recurring characters whose deaths were more final.
Colin McCormick, Cathal Gunning

https://screenrant.com/simpsons-killed-characters-canon-explained/