Yeah. You’d think he could accomplish his task more efficiently and clearly with a couple dozen bolts of fire, or some of those hailstones that burst into fire on impact.
Almost certainly not the smartest, but very much in keeping with the OP, is Lester Freamon from The Wire. Much of the fun of watching him on-screen is how he takes turns in the cat-and-mouse game of cops vs. drug-dealers: he solves mysteries in beautifully elegant fashion, and then he turns around and sets up wonderfully clever snares for the dealers. They never tell us how smart he is: they show us.
Well heck, if you’re talking about fictional cops, how can you beat Columbo?
Bruce Wayne.
IIRC, Columbo detects, and then whips the cover off the mystery at the end to reveal a neatly-tied-up solution, like a lot of fictional detectives do. Smooth Lester Freamon solves the mystery while you watch. It’s a subtle difference, but it makes him a much more impressive genius to me.
Cliff Clavin
Data.
Mais, c’est Inspector Clouseau, bien sur!
From the series Deadwood, the character that ran the brothel/gambling estabishment and if anybody “ran” the town it was him. Sometimes the dude’s sentences were so complicated and filled with meaning you felt like you needed to write them down and reread them to yourself slowly. Maybe more wise than smart?
Any anybody who can communicate with a Chinese immigrant who can’t speak any english by just doing charades and saying “cocksucker” obviously has some significant talent at linguistics (maybe Stargate should have hired him instead).
And I was going to tell him something pretty.
For examples of “inventions with the science behind them explained”, Verne’s more scientific books do that (From the Earth to the Moon, 20,000 miles, A Journey to the Centre of the Earth and others); not in a “mental processes” way, but simply because that wasn’t his style.
Phineas Fogg is surprised by having run ahead of his own calendar, but Captain Nemo is a damn genius, period, and the science behind his inventions is explained.
Oh man, I misremembered everything about that story. :smack:
So He sent the John Waynes and Bruce Willises home, and kept the dweebs and the nerds on, just in case anyone but Him wanted any of the credit? This God guy sounds like any of the power-game-playing sociopaths I’ve infrequently encountered in the workplace (few in number but all of them memorable, and not in a good way).
You might possibly be thinking of *The **Great *Brain, the titular character of which is a possible candidate for this–he is portrayed as a very bright and precocious but somewhat flawed child, but not superhuman. The portrayal seemed very reasonable. This book is a beloved classic that has been in print for the past 50 or so years, though.
Sounds like a different book. In the one I read, the genius was an adult working for the CIA or some similar agency, and could outthink not only people, but computers. And I guarantee that it was not a classic.
Possibly the winner, however, would it qualify since Data isn’t human. (of course that was never specified by the OP, but one would think a learning android would always take all and not be qualified) 
Aloysius X. L. Pendergast, from the Preston and Child series.
I love Doctor Who, but I don’t think the Doctor qualifies for this thread at all. Even as a kid, I was disappointed that we were told how brilliant he was (usually by him!) more than we ever saw it. He certainly knows a lot about his universe, but we rarely see him do anything impressive with it. He usually wins through pluck more than anything, and most of his “problem solving” consists in saying "Of course! Why didn’t I see it all along?"rather than actually deducing anything. And far too often, he simply “remembers” which previously unmentioned alien species has all of the antagonist’s traits and what it takes to defeat them. The fact that it took him so long to remember (and doesn’t go look it up) doesn’t make him look too smart, either.
Depending on how you define “fictional,” I’d consider the winner to be John Nash from the movie “A Beautiful Mind.” There was a real John Nash, of course, but the movie is historical fiction based on, but not beholden to, the facts of his actual life. Ron Howard put considerable effort into successfully showing the audience how the fictional Nash’s mind worked and how that thinking contributed to both his genius and his madness.