There are several supposed origins to this word. The earliest recorded use of this expression has been traced to the Boston Morning Post edition of 23rd March 1839. It seems to have been an example of a wrong abbreviation, and supposedly stood for “oll korrect”, meaning “all correct”.
Another story says that in 1840, the Democrats in New York created a body called the Democratic OK Club to support their candidate Martin Van Buren. “OK” here actually stood for “Old Kinderhook”, his birthplace in the state of New York.
But the most common and accepted origin is attributed to a spelling mistake made by Andrew Jackson during the presidential campaign in 1828. He wrote “ole korrek” on a document which contained the acquittal of a condemned man.
In 1932 it was officially included among the international terms for radio broadcasting. Later, during the Second World War, the American army used “O Killed” to refer to “zero killed”.