Cast the Expert

The thing about actors is that most actors are actors. While they are expected to portray fictional characters engaged in a wide variety of occupations, they rarely have the experience to be truly skilled in everything that the character does in the story. Generally, this isn't a problem. Enough skills can be acquired to fake the job through training from an expert, and for particularly complex tasks a Stunt Double, Talent Double, or Voice Double can be used.

However, on rare occasions, a person, sometimes even a non-actor, will be cast in a role partly because they already have skills from a non-acting work experience or a major hobby that are relevant to the role they are being asked to portray. Examples include both extras and main characters. If the extras are soldiers assigned to the production by the military, it is probably evidence that the film is Backed by the Pentagon. Compare to The Cast Showoff, where scenes are added to an actor's role to give them a chance to show off a talent, and Irony as She Is Cast, when actors are required to display Stylistic Suck in a talent which they are actually quite skilled at.

This trope only refers to someone being cast as a fictional character or as a fictionalized potrayal of a real person. Reality TV, game shows and the like do not count. Neither do non-fictional informative shows hosted by experts in their field, as it is not only normal but pretty much required that, for example, someone that hosts a home improvement show should know something about home improvement.

This is one of the possible methods of using Meta Casting to give added depth to a production.

Compare Non-Actor Vehicle and Autobiographical Role.

Examples of Cast the Expert include:

Fictional examples

Live Action TV

Skippy the Bush Kangaroo: In one of the episodes, a movie director decides to cast Heroic Pet Skippy as a Heroic Pet, which results in Skippy saving an actor for real when something goes wrong.
Family Matters: In "A Ham Is Born", Carl Winslow moonlights as a security guard at a movie studio where a police drama is being filmed. The movie director is annoyed at Carl's opinion of a film scene until Carl mentions his 20-year experience as a Chicago police officer. After Carl demonstrates the actual procedure for arresting criminals, the impressed director decides to cast Carl Winslow as the new leading protagonist of the film. Ultimately, Carl quits his career as a film star because he, as a married man, refuses to kiss the leading actress, even if it was only part of the movie storyline.
On Bones one of the actors in the Film of the Book of one of Dr. Brennan's novels studied to be a scientist, and was hired because the Techno Babble didn't scare him off. This becomes useful when it turns out a real murder had taken place on set, and they needed additional help examining the body.

Real-life examples

Film

Almost Angels - The Vienna Boys Choir provided many of the boys that played Vienna choirboys in the movie, though the lead parts were played by child actors with their singing voices dubbed.
Anatomy of a Murder - Judge Weaver was played by Real Life judge Joseph N. Welch.
Beverly Hills Cop. The role of Detroit police inspector Douglas Todd was played by Real Life Detroit police detective Gilbert Hill.
Black Hawk Down: In wide shots, those were actual Army Rangers fast-roping from UH-60s.
Blood Sport cast a lot of real-life martial artists as the tournament contestants. Notably, the Muay Thai fighter in the semifinals is Paulo Tocha, one of the first western Muay Thai experts.
Full Metal Jacket, R. Lee Ermey was hired to advise on the film's portrayal of a US Marine Corps instructor, but was eventually just given the role.
Going My Way - The Robert Mitchel Boychoir provided the boys that played the part of the parish choir.
Les Choristes - All the boys in this film about the creation of a choir at a Boarding School of Horrors are members of the Real Life choir Les Petits Chanteurs de Saint-Marc, including choir member Jean Baptise Maunier playing a Pierre Morhange, a boy with an exceptional singing voice.
Secretariat -Ron Turcotte was played by a jockey named Otto Thorwarth.
In Seabiscuit, George "the Iceman" Woolf is played by real-life Kentucky Derby-winning jockey Gary Stevens.
The Lord Of The Rings
- In addition to the lead actors who were trained on horses, and numerous digital extras, the Riders of Rohan were portrayed by regular horse riders from all across New Zealand who came with their own horses to act as extras.
- For The Return of the King, The New Zealand Army provided extras for the final battle in front of the Black Gate. Behind the scenes commentary on the DVD's makes note of how good they were as following directions and setting up formations, as how much enthusiasm they brought to the combat scenes.
ET the Extraterrestrial - The doctors are real doctors. The commentary mentions that this was because actors wouldn't quite speak as if they had been using the proper terms for years because, well, they hadn't been.
Eddie Bunker lived as a criminal and thief many years before becoming a writer. He was later cast as Mr Blue in Reservoir Dogs.
Audie Murphy, war hero and movie star, who played himself in the movie of his auto-biography To Hell And Back. He also played a civil-war solider in Red Badge Of Courage.
Ivan the Terrible Sergei Eisenstein used actual Soviet soldiers for the battle sequences, which kept them from going to actual combat during World War II.
The Enemy Below. Many of the sailors on the destroyer escort were Real Life U.S. sailors provided by the Defense Department. Likewise, the person playing the ship's chief engineer was the ship's actual commanding officer.
In The Best Years of Our Lives, Harold Russell, a man who had lost both hands in World War Two, was cast as a man who had lost both hands in World War Two. He did such a good job he won an Oscar, despite never having acted before.
In Black Swan, the man playing Natalie Portman's dance partner was her Real Life dance instructor for the film, although he doesn't have many lines.
In Grosse Pointe Blank cast Benny the Jet, a legendary kickboxer as well as Cusak's personal trainer, has a role as an assassin.
The guy James Bond pursues in the Le Parkour scene at the beginning of Casino Royale is actually one of the inventors of Le Parkour.
Banlieue13 (re-dubbed as District 13) features the other founder of Le Parkour as the main protagonist.
In Million Dollar Baby, Maggie's opponent in her final match was played by Lucia Rijker, a champion female boxer in Real Life.
In the film Requiem For A Heavyweight the eponymous heavyweight's final boxing match (at the start of the film) is against Cassius Clay, whom you might know better as Muhammad Ali. Ali's not just "the opponent," he actually has some in-character lines. At the end the heavyweight is forced into a humiliating wrestling match against the real life professional wrestler Haystacks Calhoun.
As could be expected, the Rocky series has cast several real-life boxers, usually in bit parts. The most prominent ones are the main opponents in Rocky V and Rocky Balboa, played by Tommy Morrison and Antonio Tarver. Furthermore, in Rocky III Rocky is in a boxer-vs-wrestler bout with "Thunderlips," played by Hulk Hogan. Hogan was a Monster Heel at the time, as is Thunderlips.
The Lost Skeleton of Cadavra—a parody of 1950's B Movies—references this in a roundabout fashion. Dan Conroy is an actor, but he plays the character of Ranger Brad as though he were an actual park ranger who got talked into playing a role in the movie because he had his own costume.
When Disney did Brother Bear, they went to Angayuqaq Oscar Kawagley for advice on the Inuit language. They liked the way he spoke Inukituk so much, they created a narrator role for him.
The film Act of Valor takes this Up to Eleven. Nearly every credited actor is enlisted in the United States Military, many of them actual Navy SEALs - who will go uncredited because they are, well, Navy SEALs.
The paramedics attempting to resuscitate Murphy in RoboCop were played by a real-life trauma team. They were allowed to improvise their lines, and on the DVD commentary the writers mention how it turned out better than what they ever could have thought up. One reason it worked so well is that the image of a trauma team working on a dying man in such a calm, emotionless, business-like manner feels incredibly creepy. Most people expect the ER team to act like they do on TV.
Many of the military extras in the Transformers series are actual military. In several cases, they didn't even have a script beyond Michael Bay telling them to say and do what they'd do in the situation.
Professional ice skater Lynn-Holly Johnson was cast in the lead role in Ice Castles, which was her film debut. Presumably, it was easier to teach a skater to act than to teach an actress to skate at the level required for the character.
In the James Bond film For Your Eyes Only Lynn-Holly Johnson plays an aspiring Olympic skater.
In the Thai film Beautiful Boxer (based on the life of Parinya Charoenphol aka Nong Thoom) the title role was filled by real life Muay Thai fighter Asanee Suwan.
Miracle cast actual college hockey players as members of the 1980 US Olympic team. Special mention goes to Billy Schneider, who played his father, Buzz.
Slap Shot had a number of minor league hockey players among its cast, including the actors who played the (in)famous Hanson brothers.
Any Given Sunday featured NFL Hall of Famer Lawrence Taylor as one of the Sharks linebackers.
Olympic gold medalist Nastia Liukin had a small role in Stick It, winning the uneven bars competition in the (rigged) final meet. Tricia Skilken was played by Tarah Paige, a former elite gymnast. And the gymnasts who compete in the Classic and at Nationals are virtually all competitive gymnasts, including many notable NCAA gymnasts and Olympians Allana Slater and Mohini Bhardwaj.
When the President's limousine is flipped over by a nuclear blast in The Sum of All Fears, he is rescued by a squad of actual Marines.
Richard Todd, who played Major John Howard in The Longest Day, was a paratrooper and veteran of the actual D-Day landings.
Grindhouse's Death Proof introduced stuntwoman Zoe Bell, As Herself.
Ronin featured world-class figure skater Katarina Witt as a Captain Ersatz of herself - the championship count given for her character in the film is her actual championship total.
Many of the SEAL team members in The Rock were played by the (retired) SEALs who also advised on the film.
A few of the players on both teams in the 2005 remake of The Longest Yard are actual retired NFL players, such as Michael Irvin as a wide receiver for the inmates' team and Bill Romanowski as a linebacker for the guards' team.
Titanic: All the crew aboard the research ship and its submarine are, well, actual research-ship-and-submarine crewmembers. Cameron hired the Akademic Mstislav Keldysh to visit the wreck, and kept them on payroll for use as set and extras once the production phase started.
A minor example in Airplane!. The screenwriters wrote lines for the two black characters who "only speak Jive". The actors who were cast in the roles pointed out that all the lines were ridiculous and were allowed to improvise their own dialogue.
Danny Trejo spent his early years as an armed robber and heroin addict, before being sentenced to 15 years in prison. Upon his release, his friend Eddie Bunker was working on a movie set and mentioned they needed someone who could play a big, scary Mexican thug. Trejo got the part, and has played similar roles more than a few times since.

Live Action TV

The Choir - The BBC TV miniseries adaptation casts St Paul's Cathedral chorister Anthony Way as a chorister for the fictitious Aldminster Cathedral Choir.
Law & Order: Attorney and politician Fred Thompson played the district attorney for several years, though it should be noted that he also had prior acting experience playing the roles of senior government officials, so this would be a cross between Cast the Expert and Typecasting.
- Ed Bogdanowicz, a retired ESU officer, played an ESU officer in 13 episodes.
Dennis Farina, an ex-cop, plays cops on Crime Story and Law & Order in addition to many film roles.
Homicide: Life on the Street - Gary D'Addario, a retired police commander, inspired the character Al Giardello, and played a recurring role as QRT head Lt. Jasper.
The X-Files episode "The Amazing Maleeni" features two stage magicians, both played by actual stage magicians.
Generation Kill: Rudy Reyes of was attached to the project as an expert, but the actor playing him suddenly became ill, so he simply played himself. It helps that he already looks like a GQ model.
NYPD Blue consultant and former New York detective Bill Clark was seen a few times as a cop.
Andy Buckley, who plays former-CFO David Wallace on the US version of The Office, is a Real Life stock-broker.
Pauley Perrette studied sociology and criminal science before becoming an actress and playing forensic specialist Abby Sciuto on NCIS.
John From Cincinnati: A TV show set in the surfing community. Keala Kennelly, who plays Kai, is a well-known professional surfer who set the record for riding the largest tow-in wave by a woman. Greyson Fletcher, who plays Shaun Yost, is a fourth-generation surfer whose drug-addicted father revolutionized the sport in the 80s with "aerial"-type tricks and whose grandfather was a defining legend of the previous-generation surf community, on top of being a professional skater himself. Greyson's character Shaun is a third-generation surfer whose drug-addicted father revolutionized the sport in the 80s with "aerial"-type tricks and whose grandfather was a defining legend of the previous-generation surf community. He was originally brought in to act as a consultant on skateboarding and surfing culture, but was eventually cast as one of the main characters. His wooden acting skills did not help the series land a second season.
Stargate SG-1 often had actual members of the military on screen. Also the reason Sgt. Siler spends most of his appearances being electrocuted, blown up and hurled around is because he's played by the show's stunt coordinator.
Power Rangers regularly casts martial artists and gymnasts in the main roles.
A few episodes of Numb3rs has Bill Nye play a scientist.
TV reporter Clarice Tinsley has played a TV reporter on Wishbone and Walker, Texas Ranger.
Glee: Heather Morris was a dance instructor for the cast until they decided to add her in as Brittany.
Mayim Bialik, who plays Amy Farrah Fowler on The Big Bang Theory, holds a Ph.D. in neuroscience, while her character is a neurobiologist.
On CSI, assistant coroner David "Superdave" Phillips is played by David Berman, who worked as a coroner for a time in real life. Berman is also a consultant on the series.
The villainous magician in the Lois and Clark episode "Illusions of Grandeur" is played by Penn Jillette, of Penn & Teller.
In most of the large-scale incidents on Emergency where units other than Engine/Squad 51 appear, the other firefighters are actually firefighters. Similarly, Engine 51's driver Mike Stoker was played by Los Angeles County firefighter Mike Stoker, the captain in the first season was an LACoFD captain, and the uncredited dispatcher was really a county dispatcher.
The low-budget 80s action film Killpoint is mostly memorable for using real police officers in several scenes, including a S.W.A.T. team.
R. Lee Ermey played another drill instructor in the sci-fi series, Space: Above and Beyond.
Retired Marine Captain Dale Dye has played a number of soldiers, including Colonel Sink in Band of Brothers, a Marine officer in Space: Above and Beyond and a Resistance officer in Falling Skies he plays an officer directing the resistance. He also ran the boot camp for the actors in Band of Brothers.
In an episode of Battlestar Galactica that called for a musician in a major part, they came close to casting the series composer Bear Mcreary. They went with someone else after the audition, but it came very close to fulfilling this trope.
Summer Glau was actually discovered this way. Glau, who is a trained dancer, was originally cast as a ballerina in an episode of Angel.
- In the Buffy the Vampire Slayer episode "Once More With Feeling" Hinton Battle (Broadway performer and choreographer) was cast as the demon Sweets.