A pair of AlwaysIdenticalTwins with one stronger in some way (more intelligent, quicker, more athletic, etc.) and the other one weaker (less motivated, is the disappointment, inferiority complex).

The plot starts with the stronger twin dead or dying. The weaker twin mourns his brother's passing, but suddenly finds that he is thrust into the limelight and forced to TakeUpMySword and assume the mantle of his brother since he's a SuspiciouslySimilarSubstitute. Often, this is due to his genetic make-up being exactly the same as his brother's, and hence, despite the apparent lack of suitability (his lack of confidence, weakness of character, or some other perceived weakness), he is the only possible candidate due to his genetic likeness.

Often the character suffers as the AngstySurvivingTwin but has no choice in the matter as he is the BackupTwin due to his DNA sequencing being exactly like his dead brother's and is essential to the plot moving forward.

Also, this is usually a perspective flip of BackupTwin shown from the perspective of the people who knew the original and recived the back up. This is where the backup is the main character.
* ''Manga/{{Touch}}'' has this as its premise.
* In ''Manga/{{Basara}}'', Sarasa disguises herself as her brother to fulfill his destiny for him after he dies. Genetics are not involved, but a prophecy that was told for both of them (but assumed to be about her brother) could be said to have the same function.

* In ''Film/EagleEye'', Shia Lebouf plays a set of identical twins, but the main character is a 'failure' whose twin brother works on a top secret AI project called ARIIA. The brother was killed in an accident in the film. The main character is mysteriously 'activated' by the AI as his identical DNA is crucial to unlocking the AI from a state of inability to act.
* In ''Film/{{Avatar}}'', Jake is paralysed from the waist down; he survives his twin brother, who works on a scientific mission to Pandora and has a Na'vi avatar which only a genetic equivalent can use. Jake's asked to take up his brother's avatar (otherwise it's a waste of an investment), but instead, Jake sides with the Na'vi.
* In the Chris Rock vehicle ''Film/BadCompany'', a CIA agent dies in the middle of an important undercover operation, and the CIA call on his separated-at-birth twin brother, an immature hustler, to keep the cover identity alive.

[[AC: {{Live Action TV}}]]
* ''Series/OnceUponATime'': In the first season episode "Shepherd," when Prince James is killed before he fights a Dragon so King Midas will reward his kingdom with gold, his twin brother David is quickly adopted and masquerades as him. Averted in that David was both a better fighter ''and'' prince than James.

[[AC: {{Literature}}]]
* In the Creator/RobertAHeinlein book ''Literature/TimeForTheStars'', the Long Range Foundation is sending GenerationShips to the stars, and to overcome the difficulties of time-dilated, luminal communication, they take advantage of the occasional ESP of identical twins. The hero lives in the shadow of his more out-going, adventurous brother, but ends up going to the stars when his brother breaks his leg skiing.

[[AC: VideoGames]]
* One of the core themes of ''VideoGame/{{Mother 3}}''. After [[spoiler: Claus goes missing, Lucas]] is the only one left to [[spoiler: pull the seven Needles and awaken the Dark Dragon]]. However, there's no mantle to take up: the mission is revealed long after [[spoiler: Claus' disappearance.]] One instance where the fact that he's a twin is relevant is when [[spoiler: Lucas is mistaken for the Pigmask Commander, granting him and his friends access into Thunder Tower]].