During the heartbreaking scene in which Big Bird and every kid watching was ripped, kicking and screaming, into adulthood, it was revealed that Mr. Hooper willed his store to his friend David, played by actor Northern Calloway. David was a rising show favorite with era-appropriate sideburns who was always eager to cheer you up with a song, and he was dating Maria, which, let's face it, is basically winning the Sesame Street lottery. Though it's not like she had a lot of other guys with flesh and working anatomy to choose from. It's only natural that David would be chosen to fill the hole that Mr. Hooper left in our hearts.
Now, we're not going to suggest that the Sesame Street shopkeeper role was cursed somehow, but it wasn't long before Northern Calloway had some kind of tragic mental breakdown. He would start fights with his co-workers that eventually became so violent that he actually bit someone. So his off-screen persona was less Elmo and more Oscar (look, we're trying to keep this light, here).
"How about I tell you how to get my foot in your ass."
And it's not like the producers of the show didn't have any warning that Calloway was unhinged. In 1980, he had beaten a woman with an iron rod before going on a one-man rampage through the streets of Nashville, smashing windows, wrecking cars, and mugging people (he reportedly wasn't wearing pants). Calloway escaped charges on the testimony that he'd suffered a "one-off nervous breakdown" and it would never happen again. (It happened lots again).