Without great characters, every TV show would crash and burn. It's the personalities and the way they develop over the course of a show's run that give its story meaning, and allow the audience to sink away into the world that's been created.
For the most part, these great characters are the show's centre, the protagonists who appear throughout every episode (or close enough). But there is another kind of brilliant character in the big world of the small screen, and that's those who appear just once, making a strong impression before disappearing again.
Such is the case with the following 10 characters, each of whom appeared on their respective shows for a fleeting but memorable one-episode visit.
From supernatural thrillers to classic prestige dramas and beloved sitcoms, these shows were already pretty damn great, but with the brief injection of these powerful personalities became even better. Many of them, in another world, would have stuck around for a longer stint.
With that in mind - and a final warning about spoilers - here are 10 great TV characters who only appear in one episode.
10. Lucille Smith - The Walking Dead
Before appearing in the flesh during the season ten episode "Here's Negan," Lucille (Hilarie Burton) was frequently spoken about, but was more of a plot device than a real person, in place to give Negan (Jeffrey Dean Morgan) a backstory and depth outside of his charismatic, cultist persona.
When she finally did appear, in a flashback episode detailing the married, pre-apocalypse life of the nefarious Savior leader, Lucille was a tragic, haunting joy, her loving relationship with Negan an emotional high point in a show with many. Suffering from cancer, she gave Negan a reason to live whilst being a powerful, lived-in character of her own.
That she was played by Dean's own wife made Lucille's debut all the more affecting, injecting her and Negan's calamitous love story with a touching air of authenticity and intimacy. Having her for just one episode was an excellent creative decision, one that packed an almighty punch difficult to shake.