Who Made That Emoticon?, article.
You don't think about that somebody has invented something as omnipresent as that, it's like "who invented oxygen?". But Scott Fahlman did it, though he's also a researcher in AI.
By the way, not so long ago a friend misunderstood something I wrote because I used colon-bracket instead of colon-dash-bracket. She simply did not recognize that as a smiley face. And I think the full icon is slightly clumsy to type, what the shift key being used for the first and last character, but not the middle one. So now I have a macro which types a few spaces and then the full smiley face. So I just hit control-right-bracket: :-)
When I first started on the Net, I was against them as many people are, they don't seem "literary" enough. But heck, most scribbles over the Net is *not* literature anyway, are they? They are more like conversation. And after somebody took a very risky joke literally back in 1997, I started using them.
If you think about it, it's just like conversation. If you are talking to a friend or two who you know well, you can make a tricky joke with a straight face. But if you're talking to a stranger, you aren't familiar with his sense of humor (or not), so you automatically smile when you do it, to show you're joking. The smiley face is exactly that, and it's a brilliant invention.