How He Died: Actor Will Lee who played Mr. Hooper died in real life and instead of recasting the role or writing him off in some other way, "Sesame Street" used it as a teaching moment for children about death. That being said, I don't think they ever gave an explicit cause of death.
Why I Was Sad: I was three and he was the first person I think I was aware of having died. Plus, Big Bird was my favorite character and he was very, very broken up about Mr. Hooper's death, so my little toddler heart hurt for him too.
How Sad Was I? I still remember that episode like it aired yesterday.