The Thin Man (1934)
The Unlikely Leading Man: Pennsylvania native William Powell, who here plays sleuth Nick Charles.
A retired detective, he attempts to get to the bottom of a murder case (and a few bottles) with the help of his wife Nora (Myrna Loy).
How He Got The Part: WS Van Dyke's film is eccentric to say the least (Nick and Nora enjoy a drink or five), and Powell's ability to rinse every scene for its dramatic wit was perfect for the film's tone.
He also shared fantastic chemistry with Loy - so much so that they'd make 14 more films together.
Batman (1989)
The Unlikely Leading Man: Michael Keaton. Despite the fact that director Tim Burton was under studio pressure to cast a big action star as Batman, the filmmaker went with Keaton, who he'd just worked with on Beetlejuice .
Keaton's casting resulted in 50,000 'protest letters' being sent to Warner Bros by irate fans who felt 'comedy actor' Keaton didn't have the range to bring real darkness to the Bat.
How He Got The Part: Burton stuck to his guns and Keaton read graphic novel The Dark Knight Returns to get an idea of tone.
He'd end up becoming a defining screen Bat.
Stranger Than Fiction (2006)
The Unlikely Leading Man: Will Ferrell, who had mostly only made broad comedies prior to Stranger Than Fiction as part of the Apatow and Saturday Night Live p osses.
Here, he's cast in his first proper 'serious' role as a man who starts to hear his own life being narrated - and then the narration predicts his death.
How He Got The Part : It was down to director Marc Forster, who decided to cast a comedian in the dramatic role in order to hit the film's various beats.
Of course, it helped that Ferrell turned out to be able to pull off the drama with flying colours.
Ghostbusters (1984)
The Unlikely Leading Man: Bill Murray as ladykiller Dr Peter Venkman. Admit it, when you envision a movie ladykiller, you think of somebody like George Clooney.
Which is definitely not Murray's look. Thinning hair, pock-marked skin, sleepy eyes. There's a reason he didn't play the romantic lead until Groundhog Day.
How He Got The Part: Aside from the fact it was basically written for him, Murray's got charm by the bucket-load - and the fact that he looks unconventional is all part of the act. Venkman thinks he's a ladykilling stud, even though he clearly isn’t.
The Public Enemy (1931)
The Unlikely Leading Man: James Cagney, a stage actor who attracted acclaim for his theatre work before he attempted to break into movies.
Despite the fact that he didn't have the conventional looks of a leading man, Cagney's dedication and unremitting energy meant he was soon starring in some of Warner Bros. biggest films.
How He Got The Part: Though short and "odd-looking", Cable's interpretation of his character blew producers away, and they decided to take a risk on him. A leading man was born…
The Graduate (1967)
The Unlikely Leading Man: Life magazine joked that "if Dustin Hoffman's face were his fortune, he'd be committed to a life of poverty", but that didn't stop Hoffman landing the lead role in The Graduate, the biggest film of 1967.
How He Got The Part: When he was asked to perform a love scene with Katharine Ross during his audition, Hoffman's awkwardness was so right for the role that director Mike Nichols cast him, despite (ahem) stiff competition.
Sure enough, Time called him emblematic of "a new breed of actors" and Hoffman quickly shattered ideas of what a leading man should be. Without Hoffman, it's likely we'd never have Ryan Gosling…
Foul Play (1978)
The Unlikely Leading Man: SNL alum Chevy Chase. He plays Lieutenant Tony Carlson, who finds himself working alongside a shy librarian (Goldie Hawn) on a bizarre case.
How He Got The Part: After his grandstanding work on Saturday Night Live , Chase could do pretty much whatever he wanted - yes, even a comedy with Goldie Hawn.
He pulled off his first "real acting" gig (his words) and then National Lampoon came along…
Boys Town (1938)
The Unlikely Leading Man: Golden Age leading man Spencer Tracy, winner of two Oscars and seven further nominations - despite not being what we'd called conventionally attractive.
In Boys Town, he plays Father Flanagan, who builds a sanctuary for troubled men.
How He Got The Part: The role didn't exactly call for a stud muffin, but Tracy had also received rave reviews for his role in San Francisco , which helped.
Also helping matters was the fact that he was 'owned' by MGM, which could cast him in whatever it damn well pleased…
Knocked Up (2007)
The Unlikely Leading Man: Muppet-y Apatow regular Seth Rogen, who was recruited by his Freaks & Geeks producer to play stoner Ben in this comedy drama.
That despite having only ever played supporting roles in other Apatow productions (and Donnie Darko ).
How He Got The Part: "He was born as a fully-formed comedic personality," Apatow has said, which goes partway to explaining why he gave Rogen the lead in the film.
It also helped that you basically believe Rogen in a stoner role no questions asked - he could play it in his sleep.
Infamous (2006)
The Unlikely Leading Man: Stage actor Toby Jones, who's made a name for himself as a man who frequently heads up outstanding movies - including this film as Truman Capote.
See also: Berberian Sound Studio.
How He Got The Part: Well, he sort of already looks like Capote (when in full costume), and though Philip Seymour Hoffman also played him, Jones' portrayal is just as brilliant.
