Originally came from Korean. The Korans use the ㅋ(won't show up here); symbol to represent laughter. In StarCraft, using the Korean writing system isn't allowed. So, unfortunately for these poor koreans, they had to express laughter somehow.
ㅋ(won't show up); is the hard k, (when pronouncing). It ended up being romanized to "kekekekekekee"
an expression (typically used by the Koreans; however it is often used by everyone) that suggests extreme happiness or of being in the state of excitement
Fred: What happened to you last night at the party?
Bob: KeKe, I got laid, man!
The noise commonly associated with the kitty face, as used by wordmako/word during Counter-Strike matches with clan Equipoise after especially good/farcical play.