This is when a new actor is brought on to play the same character as a previous actor who has left the series, with no explanation for the switch given to the audience. Named for the famous Darrin swap case: Dick York to Dick Sargent, on Bewitched.

Sargent-York became a notable phenomenon only with the rise of series television. Prior to TV, there was no expectation that a role in a theater production would be played by the same actor. It was, and still is, assumed that any production of a particular work would seek out whatever actors it wanted for the roles, and a single production can feature different actors in the same role on successive nights.

However, TV broadcasting made a bond between a role and a particular actor. Television audiences, unlike theater audiences, found it more difficult to suspend their disbelief in this respect. Maybe this was because reruns existed which would forever tie the appearance of a character to the actor that played them. Or maybe because a TV series, however long, is still perceived as a single, continuous narration — as opposed to multiple performances of a theater play.

In daytime soaps, there are several standardized ways this is done:

1. The new actor takes over with no announcement. In this variety, the actor is playing a character who has not recently been on the show. The audience is initially unaware that this person is the character we know, as his/her first interactions are always with characters who have joined the show since he left. Then someone he/she knew addresses him by name, and we are surprised. Though rarely seen outside daytime, this was done on CSI in the episode "Hollywood Brass", in which Brass's daughter was played by a new actress with a different hair color.
2. The new actor takes over a major recurring character, and the characters make a point to address them as such from the very beginning of the episode.
3. The first shot of the new actor will be accompanied by a short narrator announcement explaining that "the part of (character) will now be played by (new actor)." This is a more common method in telenovelas.

Contrast The Nth Doctor, which is the trope for cases where a character's new voice and appearance are explained in-universe. If there's a Time Skip and most of the cast remains the same then it can be a Time-Shifted Actor if the age difference justifies the particular change. For long-term cast attrition in general, see Long-Runner Cast Turnover. Flashback with the Other Darrin is a subtrope where a previous scene is reshot with the new actor.

This often is the case for spinoff series and video game versions of animated films. Celebrities typically do not reprise their roles in these cases, either because the producers cannot afford them, or because they work solely in films.

For obvious reasons, this phenomenon is much easier to hide in animated works, where actors aren't actually seen onscreen. In these cases, it might happen to a character who was originally played by a celebrity guest star who would be too expensive to hire for a regular or recurring role, necessitating the casting of a professional voice actor (or an established member of the regular cast). For example: Akira in The Simpsons was originally played by George Takei in a guest role, but by Hank Azaria in all subsequent appearances; and Roger "Booda" Sack in King of the Hill was originally played by Chris Rock in a guest role, but by Phil Lamarr in all subsequent appearances.

Unsurprisingly, this tends to be the cause of many cries of They Changed It, Now It Sucks! from the fandom, especially if the previous actor had been associated with the character for so long that they're considered to be the actor for that character. Sometimes though, the new actor can be wholly embraced by the fandom, with the new actor being regarded as the actor instead of the previous one. Unsurprisingly, when these two sides meet, the results tend to be predictable.

Compare Suspiciously Similar Substitute (when the characters have different names but are otherwise meant to be the same), Fake Shemp, The Other Marty, Obvious Stunt Double, Same Character, But Different (when there is a change in the character, without a change in creator). Directly related to Character Outlives Actor. Contrast with You Look Familiar for when the actor returns as a different character in a later installment. Can be Hand Waved via Direct Line to the Author. Often subject to Replacement Scrappy-ism. Or on the other hand, look to The Pete Best when replacement surpasses the original in popularity. Often done with Continuity Reboots. Occasionally explained away with Magic Plastic Surgery. Usually the replacement is a Poor Man's Substitute.

Defiance of this leads to Role Reprise. If the original actor returns to the role later on after being recast, see The Original Darrin.

Examples:

• Anime & Manga
• Comic Books
• Cross Medium
• Film
• Live-Action TV
• Puppet Shows
• Video Games
• Web Animation
• Web Original
• Western Animation