Actors usually aren't the same age as the characters they play. That's just part of the craft. Maybe they're playing the part over a long period of time, maybe they're reprising the part in an earlier time period. But this creates a problem when audiences are expected to believe an actor who is portraying a character who is a good decade or two younger than the actor who plays them.
For most of film history, the go-to tool for de-aging an actor has been makeup, to varying degrees of success. But modern innovations in CGI have allowed filmmakers to digitally de-age their actors, by digitally erasing wrinkles, mapping footage from the actor's youth onto the modern face, or some combination of the two. It's often a subtle variation of Serkis Folk—expect set images from films employing this technique to have actors' faces covered in plastic dots. It may also be combined with Digital Head Swap, placing the de-aged face on another actor entirely, usually a stunt double who can do things the older actor is no longer capable of.
When well-executed, it can be a nearly seamless visual effect. If done poorly, can be an example of the Uncanny Valley.
- In Waterworld, Kevin Costner forced the VFX crew to digitally hide his receding hairline.
- Pirates of the Caribbean: Dead Men Tell No Tales uses this for a flashback scene of a young Jack Sparrow.
- In X-Men: The Last Stand, CGI was used to de-age Patrick Stewart and Ian McKellen for a flashback in which they first meet Jean Grey.
- The Curious Case of Benjamin Button used CGI to make Brad Pitt look both older and younger, depending on the scene.
- In TRON: Legacy, CGI was used to make Jeff Bridges look as he appeared 28 years prior. While these scenes are few in number, CLU keeps this very appearance while Kevin Flynn appears as an older man.
- Often used in the Marvel Cinematic Universe:
- Marvel's first foray into this treatment was actually with the reverse of this effect, as Captain America: The Winter Soldier opted to age up Hayley Atwell digitally when the crew weren't satisfied with how aging her up with makeup made her look during tests.
- Ant-Man features a prologue where Hank Pym, as played by Michael Douglas, is de-aged to look as the actor appeared in Wall Street. Its sequel, Ant-Man and the Wasp, uses the same technology on Michelle Pfeiffer's Janet Van Dyne, and Laurence Fishburne's Bill Foster.
- Captain America: Civil War features a brief scene where Robert Downey Jr. is de-aged to play a teenage Tony Stark.
- Kurt Russell is de-aged to appear as a younger version of Star-Lord's father in flashbacks for Guardians of the Galaxy Vol. 2.
- Captain Marvel (2019) is set in the 1990s and used CGI to give virtually seamless de-aged portrayals of Samuel L. Jackson and Clark Gregg as Nick Fury and Phil Coulson, respectively.
- The late Stan Lee was digitally de-aged for his final cameo in Avengers: Endgame, set in The '70s. In addition, the same approach that was taken with Peggy Carter in Captain America: The Winter Soldier was used to show an elderly Steve Rogers who had returned from an alternate timeline where he got to live a full life with Peggy, after he'd returned the Infinity Stones and Thor's hammer to their proper timelines.
- The younger Hank Pym briefly returns in Avengers: Endgame, this time de-aged to look as Douglas appeared in 1970.
- The T-800 from Terminator Salvation was made by scanning a model made from a mold that was used all the way back for The Terminator then overlaying the face of bodybuilder Roland Kickinger with it, and not by digitally making Arnold's face younger.
- Terminator Genisys used CGI to have the 1984 T-800 (played by bodybuilder Brett Azar with a de-aged Arnold Schwarzenegger's face overlayed on his body) face off against one played by Arnold in his 70s.
- Terminator: Dark Fate brought Azar back to reprise his role as a T-800 circa 1998, with Maddy Curley as a young Sarah Connor and Jude Collie as a young John, also via Digital Head Swap.
- Blade Runner 2049 used this for a scene where a recreation of Rachael interacts with the aged Deckard.
- The Irishman uses this for long stretches of its runtime, allowing the septuagenarian Robert de Niro, Joe Pesci and Al Pacino to play characters in their 30s and 40s.
- Gemini Man uses this to show an assassin played by Will Smith face off against a much younger clone of himself.
- It: Chapter Two uses this on flashbacks of the younger Losers from It.
- This is used in Grudge Match to show early matches between Billy "The Kid" McDonnen (Robert de Niro) and Henry "Razor" Sharp (Sylvester Stallone).
- Star Wars:
- Rogue One, which was set just before A New Hope, has a brief appearance by Carrie Fisher's Princess Leia, as she appeared in that film.
- The Rise of Skywalker features a brief flashback of a younger Luke Skywalker and Princess Leia, with the characters appearing as they did around the time of Return of the Jedi. As Carrie Fisher had passed away by this point, her daughter Billie Lourd acted as her stand-in.
- Aquaman (2018) opens with a flashback that features de-aged versions of Arthur's parents, played by Nicole Kidman and Temuera Morrison. Another flashback also does this with Willem Dafoe's Vulko.
- Kingsman: The Golden Circle features a flashback with a de-aged Colin Firth.
- Pee-wee's Big Holiday used a combination of this and make-up to make Paul Reubens appear as he did in the previous Pee-wee films.
- The Hobbit: The Desolation of Smaug and The Hobbit: The Battle of the Five Armies both utilized this on Orlando Bloom's Legolas, to account for the fact that the character (being an Elf) doesn't age, but 10 real-world years had passed since the previous trilogy - which were also set 60 years after these films.
- American Pastoral uses this on Jennifer Connelly early in the film, making her appear as she did in The Rocketeer.