1. Nancy Drew, the Nancy Drew series
The original girl detective has changed quite a bit over the years, as the ghost-written heroine (sadly, no, there's not an actual author named "Carolyn Keene" penning these tales into perpetuity) has evolved significantly since making her debut in 1930. Even though the "modern" Ms. Drew comes complete with a cell phone and a hybrid car, one thing has never changed: Nancy uses her wits, smarts, and powers of observation to solve big-time crimes.
2. Leroy "Encyclopedia" Brown, the Encyclopedia Brown series
Thirty-three years after Nancy Drew made her debut, Leroy "Encyclopedia" Brown hit the shelves with his own brand of crime-fighting. A walking fount of encyclopedic knowledge, Leroy combines both book smarts and hardened experience (well, as "hardened" as things might get in ol' Idaville) to solve mysteries and bring bad guys to justice.
3. Matilda Wormwood, Matilda
Roald Dahl's eponymous girl heroine might be best known for her magical powers — that terrifying telekinesis! — but Matilda's big brain doesn't just house those kind of abilities, it's also filled with a voracious appetite for knowledge and a big love for books. In fact, it's once Matilda gets down to brass tacks and really starts boning up on her intellectual pursuits that her ability to move things with her mind goes away. Even a brainiac like Matilda only has so much room.
4. Anne Shirley, Anne of Green Gables series
The plucky and punchy Anne never hid her smarts from anyone, going toe-to-toe in intellectual endeavors with eventual husband Gilbert Blythe during their school years, fiercely pursuing her own career in education, and keeping up with her writing even when it didn't pay off career-wise.
5. Jo March, Little Women
Although all of the March girls display acumen for various pursuits, Jo is the real brain. A devoted reader and writer, Jo's dedication to storytelling keeps all the March ladies busy and engaged (the plays, you guys! Remember the plays?) and helps organize her own troubled thoughts. An early feminist who had no use for gender roles, Jo is a trailblazer and a smartypants who still inspires.
6. Hermione Granger, the Harry Potter series
The clever witch routinely puts the rest of Hogwarts' student body to shame with her (perhaps excessive) dedication to book-learning and magical perfection. Always eager to prove that Mudbloods are just as smart as purebloods, Hermione goes above and beyond in every way possible. The smartest witch in her year? How about the smartest witch of her time?
7. Sherlock Holmes, the Sherlock Holmes series
The original literary brainiac, Sir Arthur Conan Doyle's famous detective has always been able to deduce what's really going on in all manner of mysteries and crimes, thanks to his excessively logical mind and his interest in advanced sciences.
8. Professor Moriarty, the Sherlock Holmes series
But Holmes is only as smart as his nemesis, and the nefarious Prof. Moriarty has long proven to be one heck of a match for the pipe-smoking detective. The criminal mastermind may use his prodigious intellect for bad deeds (which are, quite thankfully, almost always thwarted by Holmes in the ever-increasing canon of books and stories about the duo), but that doesn't mean his brain isn't big. It's just ... evil.
9. Victor Frankenstein, Frankenstein
Dr. Frankenstein didn't intend to do evil when he crafted his monster — he was interested in science! really! — that doesn't absolve him of his crimes. If anything, it is Frankenstein's big intellect and even bigger ego that are the monsters of Mary Shelley's seminal novel. Although Victor spends his entire life in pursuit of scientific evolution (and he's got the skills to really push the world forward), it can't keep him from making some huge mistakes. Sometimes, even a big brain doesn't automatically mean its owners uses it for good choices.
10. Charlie Gordon, Flowers for Algernon
Daniel Keyes' sci-fi classic imagines what would happen if a person's intellect could be widely and wildly expanded, thanks to an experimental surgery previously only tested on rats. When Charlie, a janitor with an IQ of 68, is tested on, his intelligence skyrockets — a compelling enough premise for a story — before it suddenly plummets, forcing both Charlie and his readers to consider what quantifiable smarts really amount to.
11. Artemis Fowl, the Artemis Fowl series
The star of Eoin Colfer's series, Artemis is believed to have prodigious smarts — "the highest ever in Europe" — which he initially uses to increase his family fortune through criminal activities. The boy genius straightens up, eventually using his brain power for good (read: saving a bunch of fairies).
12. Captain Nemo, 20,000 Leagues Under the Sea
Jules Verne's antihero may be bent on revenge and destroying the British Empire, but he's not just a seafaring madman, he's a bonafide genius who built his own submarine. Again: He built his own submarine.
13. Ignatius J. Reilly, A Confederacy of Dunces
The star of John Kennedy Toole's cult classic novel may not always use his brain power for good (for one, he's a tremendous slob), but that doesn't mean that he's packed full of some powerful wit. Walker Percy, who wrote the book's foreword and helped get it published over a decade after Toole's death, describes him in loving terms: "slob extraordinary, a mad Oliver Hardy, a fat Don Quixote, a perverse Thomas Aquinas rolled into one."
14.–20. The Glass Children, the Glass stories by J.D. Salinger
If we're talking about pint-sized brainiacs, the conversation has to start and end with the Glass kids. Although we only really get to know five of the seven Glass kids — while the twins Waker and Walt are enigmas, Salinger's various Glass stories spend plenty of time with Franny, Zooey, Buddy, Boo Boo, and Seymour — all of Les and Bessie's kids are genuine geniuses. In fact, all seven of them are known to have competed on kid quiz show "It's a Wise Child," each earning enough to put them through college.
21. Ian Malcolm, Jurassic Park and The Lost World
Yes, Jeff Goldblum. Or, more specifically, the character written by Michael Crichton who then became one of Goldblum's most infamous characters. A mathematician with a special interest in chaos theory, Dr. Malcolm might be the one clever enough to make dinos, but he was smart enough to figure out how to bring the beasties down (with lots of all-black style to boot).
22. Robert Langdon, Angels & Demons, The Da Vinci Code, The Lost Symbol, and Inferno
Dan Brown's famous fictional professor uses his smarts and his training to solve the kind of mysteries that span time, place, and faith. An expert in areas like religious iconography and symbology, Langdon is another brainiac who combines big-time book learning with intuitive smarts, even when he doesn't quite like the results.
23. Ender Wiggin, the Ender's Game series
Like many other teen geniuses, Ender struggles with what his abilities really mean — is it a good thing to be in possession of a brilliant military mind if that comes with a staggering lack of empathy? But as Ender grows in Orson Scott Card's series, both his intelligence and his emotions grow ever stronger. You can have both.
Image: Warner Bros. Pictures