Ability Over Appearance

Casting agents usually have a very specific appearance in mind when casting actors to play their characters. When holding auditions there will usually be descriptions noting what the character should look like, for example blonde hair, frail frame, not too tall etc. This is also the case when casting actors in adaptations of books and video games. However, sometimes an actor who is completely different from the physical description shows up for the audition and they completely nail it. The casting directors throw the description out the window and hire this actor because of their performance. This sometimes leads to other tropes such as Race Lift, Adaptational Attractiveness and often Hollywood Homely and Hollywood Pudgy if the character was meant to be ugly but references to this weren't removed when an attractive actor was cast. It's rare but it can also happens with regards to a character's gender. Note that it isn't an example of the trope if the actor works hard to resemble the physical description of the character.

Film
""If you have a chance to have a great actor in the part, everything else is irrelevant. ""
 * In an unintentional case, Jeanette Goldstein mistook Alien S for a film about Mexican border crossers and turned up for the audition dressed as a prostitute. She ended up getting the part of tomboy Vasquez anyway.
 * Directly lampshaded by Hudson's line, "Right, right. Someone said 'alien'; she thought they said illegal alien and signed up!"
 * For the first film, while all the characters were written to be gender-neutral, Ripley was always thought of as male but of course Sigourney Weaver ended up getting the role.
 * When casting Red for The Shawshank Redemption the description was for a middle-aged Irish man with greying red hair and actors such as Clint Eastwood, Harrison Ford and Robert Redford were considered. Morgan Freeman wound up getting the part because the director "couldn't see anyone else as Red" after his audition.
 * Which had the added effect of the line - "Why do they call you 'Red'?" *pause* "Maybe it's cause I'm Irish." - becoming hilarious.
 * A twofer case in The Last Airbender - Zuko was Asian in the original cartoon and director M. Night Shyamalan considered white Jesse McCartney for the role but Anglo-Indian Dev Patel ended up getting the part from his audition tape.
 * Though according to some, McCartney already had the role but was switched for Patel early to try to stave off the upcoming accusations. This didn't help those who noticed that the only non-white star role was the quote-unquote "evil/troubled" character.
 * Some people also argue that his choice for Aang was because of this. The actor, Noah Ringer, was good at martial arts but an average actor.
 * This was also the justification of Sokka and Katara; in the series they were Inuit/Native American analogues, in the movie they were turned white. Considering how much their performances were criticized, the justification didn't hold up, to fans or critics.
 * The producers of The Lord of the Rings intended to cast only British actors as the Hobbits as Tolkien had imagined the Shire as a form of England but American Elijah Wood sent in a strong audition tape and was cast as Frodo.
 * Not quite a case of ability over appearance, since he happens to fit the book's physical description of Frodo excellently.
 * Ben in Night of the Living Dead was not written to be black and Romero claims he only cast Duane Jones because he gave the best audition, rather than to make a point or be controversial.
 * The Harry Potter films frequently cast actors this way. Horace Slughorn, Dolores Umbridge and Gilderoy Lockhart were all played by actors who didn't quite match the physical description of their book counterparts (for instance, Slughorn is meant to be short and stout, but Jim Broadbent is over six feet), but who had the attitude of them perfectly.
 * In the Thor comics, Heimdall is pretty covered up, but still visibly Caucasian. For the film, Kenneth Branagh chose to cast Idris Elba. Fan controversy over his choice led to this quote:


 * Daniel Craig got a bit of controversy when he was cast as James Bond in Casino Royale because he looked very different from the past Bonds, being derisively referred to as "James Blond." This of course all went away once the film came out and he got rave reviews. He may have invoked the trope since he refused to dye his hair black for the role.
 * Casting Quoyle of The Shipping News based on appearance would require a lot of excessive prosthetics so instead Kevin Spacey sells the role on the strength of his performance.
 * Philip Pullman had something of a reaction like this when Nicole Kidman was cast as Mrs. Coulter in The Golden Compass. The character has black hair in the books (Kidman being blonde) and Pullman said "I was wrong, she has to be blonde", Kidman having been his personal choice for the role.
 * Sissy Spacek was widely thought to be too pretty to play Carrie White, the character in the book being described as chunky, mousy-haired and covered in pimples with Spacek being a tall thin redhead with clear skin. But Spacek's Oscar nomination speaks for itself. The character was then rewritten slightly saying that she would be pretty if she made an effort to tidy herself up a bit.
 * Angela Bettis from the TV remake is another example, not really matching the book's description but giving a great performance as Carrie. Though she did work hard to match other parts of the character's description.
 * Julie Taymor altered William Shakespeare's The Tempest to have Helen Mirren play the lead.
 * Anne Rice openly protested against Tom Cruise being cast as Lestat in Interview with the Vampire but after she saw the film, she issued an apology and praised his performance. Though she did insist that Lestat's hair remain blond in the film.
 * In the Daredevil movie, the Kingpin was played by Michael Clarke Duncan. He was the best actor with the size that they could find, and even then, he had to gain some weight for the role. Ironically, the Kingpin was originally supposed to be black in the comics, but an editor thought it would be racist to have a black villain.
 * This carried over into the short-lived Mainframe animated Spider-Man series on MTV, to the point of actually having Michael Clarke Duncan voice the character.
 * The Mean Girls producers thought Lizzy Caplan was too pretty for "art freak" Janis, but eventually cast her for considering her the best actress that auditioned.
 * Hailee Steinfeld did an amazing job as Mattie in the 2010 film of True Grit, which didn't drop a single line of dialogue about how ugly she was. Similarly, all dialogue about Rooster being fat and out of shape was kept, even though Jeff Bridges barely had a visible belly.
 * Winona Ryder in Little Women is much too petite to play Jo, who in the book is described as being "like a colt" with "long limbs and big shoulders and hands". That being said it's hard to imagine another actress who can capture Jo's spirit, clumsiness and generally loud attitude as well as she can.
 * Robert Downey, Jr. is almost the exact opposite of Sherlock Holmes in appearance (as opposed to Jude Law, who rather resembles Watson) but his performance in the new film is generally considered to be very Holmes-ish, whatever other faults the film has.

Live Action TV

 * The character of Lisa in Saved by the Bell was written as a Jewish princess with the auditions calling for white females only. Lark Voorhees (African-American) got the part based on the strength of her audition.
 * Producers were reluctant to cast Amber Benson as Tara in Buffy the Vampire Slayer because she was too voluptuous for the supposedly plain girl but she won them over with her awkwardness.
 * When casting Julia in Party of Five producers wanted a relatively young actress (the character was 15 at the time) but ended up casting the 19-year-old Neve Campbell due to her strong attitude during the audition.
 * The 80s BBC Production of The Chronicles of Narnia cast four children who were nothing like the descriptions - Peter looked too young, Lucy was much older and chubbier, Susan was blonde and Edmund looked older than Peter - but they all gelled well together in their auditions.
 * Shelly of Northern Exposure was written to be Native-American but Caucasian Cynthia Geary ended up getting the part.
 * Given the time-period and the fact that Guinevere means "white" or "fair one", there were some raised eyebrows over mixed-race Angel Coulby getting the part of the future queen on Merlin. The producers said that they had looked at hundreds of potential Guineveres, but Angel Coulby was the only one that could nail the quirky, clumsy servant girl, but also "bring the queen" when the occasion called for it.
 * Series author Elizabeth George was openly displeased about the casting choice for Barbara Havers of The Inspector Lynley Mysteries - The BBC cast the lovely Sharon Small in the role, whereas Barbara is distinctly unattractive. Then George saw Small's performance in the pilot, in which Sharon absolutely nailed Barbara Havers in all her awkward, bitter, broken glory. She changed her mind rather completely.
 * Happened twice in Criminal Minds. Garcia was originally written as a middle-aged Mexican man, but when the white, blonde and very female Kirsten Vangness was introduced to the producers they had to have her and changed the part. (Her last name was later explained as coming from a stepfather.) Aaron Hotchner was supposed to be a blonde Mormon from Utah, but the part eventually went to the dark-haired Virginian Thomas Gibson.
 * Steven Moffat was adamant that he'd had enough of young Doctors, and was going to cast an actor who was at least middle-aged. And then Matt Smith auditioned, and that was that.
 * Grey's Anatomy has always been known for colorblind casting (leading to one of the most diverse casts on television,) but that doesn't mean that they didn't have a general idea of who to cast. Miranda Bailey was intended to be a blond, white women until Chandra Wilson got a hold of the part.
 * Kaylee from Firefly was originally intended to be Asian, but Jewel Staite's audition impressed Joss Whedon enough that he decided to give her the part anyway. This did have the awkward side effect of leaving no major characters of Asian descent in a universe heavily influenced by Chinese culture, however.
 * In The Suite Life of Zack and Cody, originally the parts of Maddie and London were inverted, with the blond Ashley Tisdale playing the obvious Paris Hilton expy London Tipton, and Brenda Song playing Maddie. However, when it was revealed that Brenda Song has a natural affinity for playing The Ditz, the roles were reversed. This had an unfortunate side effect, however. By having Brenda play the Ditz, it accidentally reinforced the Asian Airhead trope.
 * Chase in House was originally intended to be British, but Jesse Spencer gave such a brilliant audition that he was made Australian instead.
 * House himself is a minor example; the director had put a ban on non-American actors for the title role after hearing so many badly-done fake American accents in auditions, and decided on the British Hugh Laurie for the role before knowing this fact because Laurie delivered his lines in a flawless Bostonian accent.
 * When Pauline McLynn first auditioned for Mrs. Doyle on Father Ted, she was rejected for being too young and pretty (McLynn was in her early thirties; Mrs. Doyle was a middle-aged widow). She supposedly showed up for another audition with a bad cold - and got the part.
 * Nickelodeon had a show planned in the mid-1990s to be titled "The Mystery Files of Shelby Wink" about a teenage white girl who solves crimes, but Asian American Irene Ng impressed them so much with her audition that they re-named the show "...Shelby Woo" and altered the premise accordingly.

Theater

 * Patrick Stewart, Michael Gambon and Anthony Hopkins have all played Othello, the Moor of Venice. Although in at least one case (Stewart's), the entire play was cross-cast, making an interesting social experiment.
 * Although Hamlet is a young college student, his constant change of emotion makes him one of the most challenging roles an actor can play. Because of this, he is almost always played by a much older, more experienced actor.

Western Animation

 * Variant: when animating Aladdin, animator Andreas Deja was surprised to see the slightly chubby voice actor Jonathan Freeman was totally different from the Lean and Mean villain Jafar, but still incorporated Freeman's expressions and gesturing to the character. (and Freeman later played Jafar in theater)

In-Universe Examples:

 * When holding cheerleader auditions in Bring It On the cheerleading squad wants a girl who fits the typical cheerleader image. When tomboy Missy gives the best tryout they are reluctant to let her on the squad but she gets on anyway.
 * Which, technically, she does; thin, atheletic, hot. It was only her attitude and non-girly that turned them off.
 * A strange case with Bridget in 8 Simple Rules when she ends up getting the part of Anne Frank in the school play despite looking nothing like her. She reads the book and ends up giving a fantastic performance.
 * The picture book Amazing Grace by Marry Hoffman is about a black girl auditioning for the role of Peter Pan. It plays out exactly how you'd expect it to.