Allan Metcalf - "OK" is one of the most frequently used and recognised words in the world. It is also one of the oddest expressions ever invented. But this oddity may in large measure account for its popularity.
It's odd-looking. It's a word that looks and sounds like an abbreviation, an acronym. We generally spell it OK - the spelling okay is relatively recent, and still relatively rare - and we pronounce it not "ock" but by sounding the names of the letters O and K. ...
On 23 March 1839, OK was introduced to the world on the second page of the Boston Morning Post, in the midst of a long paragraph, as "o.k. (all correct)".
How this weak joke survived at all, instead of vanishing like its counterparts, is a matter of lucky coincidence involving the American presidential election of 1840.
One candidate was nicknamed Old Kinderhook, and there was a false tale that a previous American president couldn't spell properly and thus would approve documents with an "OK", thinking it was the abbreviation for "all correct".
Within a decade, people began actually marking OK on documents and using OK on the telegraph to signal that all was well. So OK had found its niche, being easy to say or write and also distinctive enough to be clear.
via BBC News - How 'OK' took over the world.
Martin Van Buren (December 5, 1782 – July 24, 1862) was the eighthPresident of the United States, serving from 1837 to 1841. Before his presidency, he was the eighthVice President (1833–1837) and the 10th Secretary of State under Andrew Jackson (1829–1831). He was a key organizer of the Democratic Party, a dominant figure in the Second Party System, and the first president not of British descent—his family was Dutch.
... Van Buren's unsuccessful reelection campaign in 1840 is regarded by etymologists as instrumental in the popularization of the word "OK". In the context of the campaign, the initialism was used as a nickname for Van Buren and stood for "Old Kinderhook," which was a reference to Van Buren's birthplace.
Kinderhook is a town in the northern part of Columbia County, New York, United States.
According to Woodford Heflin writing for American Speech in 1962:
"... the argument ran that the 'all correct' meaning begain when the Whigs fabricated a story to discredit the Democrats before they (the Whigs) actually knew what the Democrats meant by the expression. According to this Whig story, Andrew Jackson, the Democratic hero, was illiterate and he used the expression O.K. for Oll Korrect, which they said was his way of spelling "all correct". This story, although not necessarily told to be believed, had the effect, so the argument went, of supplying a meaning for the mysterious letters O.K. which the Democrats had not yet explained, although they were busy using the letters in headlines and shouting them in the streets.... "
The history is interesting. The Democrats, it seems, were keeping the 'Old Kinderhook' meaning secret, their own private code because this was attracting attention and arousing political interest. When the Whigs came forth with the story about Jackson, the Democrats were irked and boldly adopted the 'all correct' meaning to undo the damage by the Whigs.
First there was the Democratic Republican Party.
One faction of the party supported Andrew Jackson and it evolved into the Democratic Party. Another faction, led by John Quincy Adams and Henry Clay, was known as the National Republicans; it evolved into the Whig Party.