Super-smart fictional characters?

I need some more help today: who’s a fictional character (books, tv, film, whatever) who seems to know how everything works, and remembers lots of little details that come in handy to save the day?  Not so hands-on as MacGyver (and I’ve compared one of my characters to him before).

Thanks. (Apparently my brain doesn’t hold anywhere near the amount of information as this guy or gal.)