OK, OK, OK!

OK is probably one of the most widely used term (and not only in English). But where does it come from?
The official word is that it appeared in 1839, in some Boston newspapers, as an abbreviation for Oll Korrect (they liked to play with words in Boston then). But it really became popular during the 1840 American election, as one of the candidate's nickname, Martin Van Buren, was Kinderhook (since he was born in the town of Kinderhook, in the state of New York): he was then called Old Kinderhook.
But there are many, many more theories about the etymology of OK.