Not-So-Small Role
If you recognise the actor in a bit part, it will probably turn out not to be such a small role after all; it will be The Big Bad, or the murderer, or someone else who is a key to whatever mystery the show revolves around. Usually, their true identity is not revealed until the final act. This is often referred to as the Law of Economy of Characters in film criticism.
This is especially prevalent in dubbed anime series with Loads and Loads of Characters. Often when you have a Hey, It's That Guy! moment, a seemingly insignificant character will later end up having a large role. Even if Anyone Can Die, a character voiced by Steve Blum will rarely be Killed Off for Real (until the finale).
The converse of this would be One-Scene Wonder, where the part is small but juicy enough to justify casting a talented actor.
Subtropes
If you have an example for the subtrope, put it on those pages.
See also: Contractual Immortality, Conspicuously Light Patch, Chekhov's Gun. May be a Final Girl.
- Tru Calling: Jack Harper (played by Jason Priestly) started off a paramedic who would come in, drop off a dead body, and provided for the series what seemed to be some minor flirtation with minor flirtation. Then with the beginning of season 2, he's the anti-Tru villain who is the antagonist of nearly every episode.
- The Pretender: The two-parter "Bloodlines" stars Haley Joel Osment. Jarod must identify which one of three children is a genius. Since two of the children are unknown child actors and the last one was the lead in The Sixth Sense the year after appearing on this show, it's not hard for a post-1999 audience to guess which one it is.
- Baccano!: A seemingly ordinary guy who works on the train (played by Masakazu Morita) gets killed fairly early on in episode 2. Then came episode 9 and it was revealed that he is actually The Rail Tracer and he gets to play against the seiyuu's known roles.
- Tommy: In the film, Tommy is played by Roger Daltrey, a not-so-subtle clue that he might not be mute for the entire movie.
- Even before there was a voice actor to indicate it, Fairy Tail had one of these. Sure, Siegrain just acted like a background character who'd comment on the cast's adventures, but the first time he does this is the first page, before the cast even shows up, and even that isn't as telling as the fact that he's given the exact same character design as one of the more popular characters from Hiro Mashima's previous manga.