Sorry if this fairly obvious topic has been covered before, but I couldn’t find it through the search.
Which fictional character, including characters in cinema, do you think displays the most intelligence? I mean, as opposed to characters who are simply asserted to be intelligent, like God in the Bible.
Sherlock Holmes
Holmes is an annoying smart-ass who has the author in his lap, making sure none of his really important unsupportable feats of illogic go off the rails.
He demonstrates some intellect, but for the most part the rigged-ness of the game makes his intelligence less of a feature than it ought to be.
Naw, Moriati (spelling?) has him beat. And I mean the one from the Holodeck, not that 20th century wanker 
Moriarty.
Hannibal Lecter?
Cecil Adams.
Known Space Protectors, at least when their instincts don’t get in the way.
Depending on what we consider intelligence, Reed Richards.
Then again the OP doesn’t specify humans, therefore any God-like character would be the answer.
Actually very few; most god-like characters and gods in general aren’t portrayed as particularly bright. More tends to be made of their perceptions, like omniscience or the ability to see the future than of actual intelligence.
Lazarus Long.
Light Yagami from Death Note is up there.
Quantum Cop.
Agreed. I think of intelligence as the ability to learn and to figure things out, not the ability to peek at the answers in the back of the book.
Sam Beckett, Quantum Leap.
Has a photographic memory, an IQ of 267, seven doctoral degrees and knows seven languages. And he basically invented time travel.
Agreed. I’m not up to speed with the Ringworld series past Throne, but protector-stage humans have been able to do things like:
build artificial planets around gravity generators and decorate them with Escher-style architectural paradoxes that are also made to work using artificial gravity (Jack Brennan), and
deduce how Puppeteer stepping discs worked merely by knowing that they existed and devise a means of hijacking into one (Teela Brown). And Teela was also able to work out how to save the Ringworld using a method that she could not apply but decoy people who *could *into the right place to do it instead, effectively playing one half of her own brain against the other.
There are some interesting suggestions so far that I will have to look into. Just to clarify, I am looking for characters who are actually shown doing unusually intelligent things: making smart decisions or insightful observations. Kind of like some of Shakespeare’s characters exhibit a heightened articulateness, as opposed to Shakespeare simply asserting that they have super-high scores on some test for verbal intelligence (anachronistic, I know) or that they have used their articulateness to accomplish some incredible thing offstage. I want to actually see the intelligence in action.
Logically, Spock should be considered.
Marvin, the paranoid android from The Hitch-Hiker’s Guide to the Galaxy certainly has a high opinion of his own brainpower, or at least the sheer size of his brain. Nonetheless he does display extraordinarily intelligence throughout the book series. Quoting straight from Wikipedia, he “simultaneously manages to plan the entire planet’s military strategy, solve all of the major mathematical, physical, chemical, biological, sociological, philosophical, etymological, meteorological and psychological problems of the Universe except his own, three times over, and compose a number of lullabies”.
And of course Deep Thought, the supercomputer - who has a voice and a personality and is thus a character - solves the fundamental question of life, the universe, and everything. Which presumably makes him the smartest fictional character of all time ever. Technically he has a smarter successor (a supercomputer built into the planet Earth) but we never get to hear the Earth speak, so he or she isn’t really a character.
Holmes wasn’t nearly the smartest even of his contemporaries. Baroness Orczy’s The Old Man in the Corner or Jacques Futrelle’s Professor Augustus S. F. X. Van Dusen, Ph. D., LL. D., F. R. S., M. D., M. D. S., who was the Thinking Machine, were easily smarter and better detectives than Holmes. They haven’t lived on since they had less atmosphere and most of all less action. Holmes is known more for that than for the sometimes silly deductions.
Peter Wimsey is reputed to be quite intelligent. Ellery Queen is an all-knowing brain. Sir Henry Merrivale is a doctor and a barrister and head of Britain’s spy agency and probably the most fun to hang out with. Mysteries are filled with brainiacs.