Kek on the internet is waaay older than the_donald. There are two things I'd consider sources (although there's probably even older shit I've missed):
"Kek" is the equivalent to "lol" in korean
As far as the west is concerned, in World of Warcraft, if you were playing Alliance and a member of the Horde wrote "lol" in their language, you'd read it as "kek" (because your character wouldn't know their langage).
It's something that was started back in the old the_donald days on reddit. It basically is our euphemism for LOL (laughing out loud)
Kek on the internet is waaay older than the_donald. There are two things I'd consider sources (although there's probably even older shit I've missed):
Actually it started long before that,. It started in MMORPGs.