The entrepreneurial psychiatrist, Dr. Marvin Monroe, was killed off in The Simpsons, but the reason for his disappearance from the show didn't have anything to do with the story. Voiced by Harry Shearer, the tie-wearing character first appeared in The Simpsons season 1 but eventually disappeared and was presumed dead, at least until a surprise re-appearance.
Dr. Monroe first appeared in The Simpsons season 1 episode “There’s No Disgrace Like Home”. In the episode, Homer visits Moe’s Tavern, and worries about being a failure. But then he sees a television promo for Dr. Monroe’s Family Therapy Center, and brings the Simpson clan to Dr. Monroe for some “aversion therapy,” which involves Simpson-on-Simpson violence. In “The Call of the Simpsons”, Dr. Monroe reveals his academic findings after Homer is inadvertently mistaken for Bigfoot, and later appears as part of angry Springfield mob when Bart, under the influence of peer pressure, decapitates a statue of Jebediah Springfield. During The Simpsons season 1, Dr. Monroe also provides therapist advice on a KDBL radio show.
Dr. Monroe was conceptually killed off during The Simpsons season 7. The aforementioned Shearer reportedly didn’t like the vocal strain of performing the character lines, and series creator Matt Groening didn’t particular enjoy the “annoying” tone. The Simpsons season 7 premiere reveals that a hospital was named after the seemingly deceased Dr. Monroe, while The Simpsons season 7 episode “The Simpsons 138th Episode Spectacular” heavily implies that the psychiatrist had indeed passed away. Dr. Monroe's grave even appears during The Simpsons season 11.
But it turns out that Dr. Monroe wasn’t actually dead, at least in The Simpsons' universe. In fact, a rather enthusiastic Dr. Monroe shows up at Marge’s book release in The Simpsons season 15 ("Diatribe of a Mad Housewife"), and applauds the author for her “very psychological” book. The doc also reveals that he’d been “very sick” after Marge acknowledges that he’d been gone for quite some time. Aside from a painting cameo in The Simpsons season 28 episode "Treehouse of Horror XXVII", Dr. Monroe makes only one more appearance in the form of a ghost, which seems to confirm his untimely death.
During The Simpsons season 29 finale, "Flanders' Ladder", Bart gets hit by lightning and sees various ghosts, including Maude Flanders. Another spirit is none other than Dr. Monroe, who appears in his usual attire but with Incredible Hulk-like green skin. The collective group of ghosts ask Bart to help settle their beefs, with the deceased psychiatrist in question saying only one word during the posthumous appearance: "Beeefffsss!" As long as The Simpsons continues to air, Dr. Monroe will undoubtedly make his presence known in Springfield.