I've heard of and read about different theories, but the two that seem to hold the most water (seem to be the most accurate) are actually related: 1) The letters "OK" did stand for "oll korrect," which was just one of a group of humorous abbreviations that began popping up in American newspapers and other documents in the 1830s and 1840s. The misspellings are intended. :) 2) In 1840, Martin Van Buren was the Democratic candidate for the office of president of the United States of America, and the Democrats nicknamed him "Old Kinderhook," since he was a native of Kinderhook, New York. "Old Kinderhook" was then shortened to "OK," which the Democrats used as the name of their political club. The theory is that the Democrats got the idea for "OK" from the "OK" commonly found in newspapers at that time. This put the expression (well, abbreviation, actually) into common use and common knowledge. :)

There is a theory that the word "ok" is decended from a similar expression in a West African language brought over to America during the slave trade. "Wakay" means 'correct' or 'all right'.

calixto's version of the story sounds familiar . It should have been hence " A C " = all correct , but the guy was probably illiterate and that would have been always mixed up with " air condition " ;)

oll kontrolled. it is miss-spelled by someone, but then become common.

This tale probably never happened but once I heard that, during the US Civil War, an illiterate guy who had the job of inspecting cargo used the letters O K to indicate that the things he surveyed were "Oll Korrect".