It can be difficult to find the right actor for the right part; especially when we're talking about a particularly niche role. If you think about all the times when directors have been pressured to hire someone at the last minute, or a more famous name drops out just before shooting commences, then it's really a miracle that anything even gets shot in the first place. Add to that the ridiculous salaries of most major Hollywood actors, and honestly it's a wonder that directors don't just cut out the middle man and replace actors with slobs off the street. Yup: acting talent can come from the most unlikely of places, and there are some people who, professional actor or not, are simply instinctively able to act naturally in front of the camera. There have been plenty of cameos, and even major roles over the years, played by people who weren't actors in the first place. Some were memorable, others slotted into the background without you ever realising. The only thing these people had in common was that none of them were actors.

1. David Bowie - The Prestige

In a period movie, when you want to represent a major figure from history, sometimes you need a truly iconic celebrity to embody that role, so that the character becomes famous even in his own time. If you want an example of esoteric casting done right, then look no further than Christopher Nolan's mindbending, twist-ridden suspense movie The Prestige, which sees the late David Bowie play the part of the genius scientist Nikolai Tesla. It's a small role, but absolutely crucial to the plot, and if you ask me, Bowie does a very good Eastern European accent. Seeing him greet the magician Robert Angier, as played by Hugh Jackman, you really can believe that this is the man who makes the impossible happen.

2. Stephen King - Creepshow

Horror anthology movie Creepshow is, for the most part, a pretty light-hearted and tongue-in-cheek romp; a collaborative tribute by Stephen King and George Romero to EC comics like Tales from the Crypt, and one that will make you laugh just as much as scream. In this sequence, Romero just couldn't find the right actor to play the eponymous bumbling hillbilly in the sequence "The Lonesome Death of Jordy Verrill". Eventually, the modern master of horror Stephen King decided to fill Verrill's mismatched shoes, and played the part with such goofy enthusiasm that it's hard not to enjoy the largely-comic interlude.

3. Harry Styles - Dunkirk

Since his casting of Bowie seemed to work so well, Christopher Nolan decided to hire another pop star for an important role - namely hiring former One Direction member Harry Styles to play the part of Alex, a private in the Argyll and Sutherland highlanders. Apparently, Nolan was unaware of Style's fame as a musician when he picked him to star in his WWII epic, and hired him on the basis of his acting talent alone.

4. Catherine Scorsese - Goodfellas

In this climatic scene from Scorsese's gangster movie Goodfellas, the main trio of wiseguys, played by Ray Liotta, Joe Pesci and Robert De Niro, make a pit-stop at the house of Paulie's mother. Paulie's mother, rather than being a hellraiser, turns out to be a sweet old Italian woman, who makes dinner for the three mobsters while they have an unfortunate victim tied up in the trunk. What you might not have realsied is that Paulie's sweet little mom was played by Catherine Scorsese: Martin Scorsese's mother. Personally, I think she nailed it, don't you?

5. R. Lee Ermey - Full Metal Jacket

R. Lee Ermey is the archetypal drill sargeant; the one that everyone thinks of when they think about life in the army: barking orders and spewing profanity. Nowadays he's a common sight in Hollywood movies, usually giving some poor recruit an earful or playing a parody of himself. But way back in 1987, the former real-life U.S. Marine Drill Instructor was originally hired by Stanley Kubrick as a technical advisor, to consult about the accuracy of the marines training scenes. But Kubrick loved Ermey's foul-mouthed improvisations so much that he gladly gave him the role of gunnery sergeant Hartman.

6. Quentin Tarantino - From Dusk Till Dawn

Director Quentin Tarantino is well-known for making cameos in his own movies; but they're usually small, bit parts without much relevance to the main plot. For example, in Pulp Fiction he filled in for Steve Buscemi at the last minute for the short "The Bonnie Situation". But his role in the vampire movie From Dusk Till Dawn, which he directed alongside Robert Rodriguez, proves that he has the acting chops to play meatier roles. Here you can see him playing the creepy and deranged rapist Richie Gecko - a character so slimy and twisted that you wonder if Tarantino just wanted to spare anyone else the burden of portraying him.

7. Frank Miller - Sin City

Frank Miller is best known as one of the foremost talents of the comic book industry. He and other writers such as Alan Moore and Art Spiegelman managed to make the medium a literary one, and revolutionised the superhero genre with his graphic novel The Dark Knight Returns. When Robert Rodriguez (yes, him again) decided to adapt his gritty, neo noir series Sin City for the big screen, he cast Miller himself as a corrupt catholic priest that Marv (Mickey Rourke) executes in confession.

8. Mel Brooks - Blazing Saddles

Blazing Saddles is one of my all-time favourite comedies, perfectly skewering the clichés and conventions of the Western genre, and exposing the racist attitudes underpinning it. Here, writer and director Mel Brooks plays a corrupt governor conspiring with Hedy LaMarr ("that's Hedley!") to steal native American land - a role he plays with considerable aplomb. It's so OTT that it has to be seen to be believed.

9. Irvine Welsh - Trainspotting

Danny Boyle's adaptation of Irvine Welsh's bleak heroin odyssey Trainspotting was one that was celebrated by critics for its bleak and uncompromising realism. So who better to play one of the minor characters, namey Mickey Forrestor, a small-time dealer who provides Ewan McGregor's Mark Renton with suppositories just before he goes cold turkey, than the author himself. Here you can see Welsh himself making a cameo, meeting Renton in his decrepid Leith flat.

10. Eminem - The Interview

The Interview was one of those movies that was overshadowed by its own controversy, after the North Korean government made a huge deal of it - so not as many people saw it in cinemas as the studio hoped. It's a shame, because the film itself, which stars James Franco and Seth Rogen, it's actually really solid. But the most memorable scene is probably when Eminem appears on a chat show as himself, and subsequently comes out as gay live on television. Even though he's playing himself, he's still pretty convincing, don't you think?

Casting certainly isn't a simple process. In fact, at times it can actually be pretty controversial. For example, Deadpool and Game of Thrones actor Ed Skrein recently quit the new Hellboy movie after he was accused of whitewashing for accepting a role meant for an asian actor.

10 Movie performances from people who weren't professional actors