Television guest stars: Like the crisp, cool first weeks of fall, or the ripeness window for avocados, their time is so short but so sweet. They grace us with their presence for an episode — or a handful, if we're lucky — and then poof! They're gone.

Some guest stars appear in hysterical, one-off episodes, while others become key players in dramatic arcs. They can fill in a missing piece to a main character's back story, like Cicely Tyson's turn as Annalise's mom on How to Get Away with Murder. Or, they can pop in for a single episode just to make us laugh our asses off. They can bring their signature brand of acting to a show, or surprise us all and play completely against type — like Brad Pitt in his Thanksgiving drop-in on Friends. Perhaps most amusing is revisiting the guest-starring turns actors made before they were famous. (Walter White, what are you doing on Seinfeld?!)

Here are just a few guest stars near and dear to our hearts who we wish had become more permanent fixtures on the shows they visited.