The Oxford English Dictionary has traced the etymology to most likely be an abbreviation of "orl korrect," a form of "all correct." This was popularized when the Democratic candidate for president, Martin Van Buren, ran for re-election in 1840. He claimed that it stood for "Old Kinderbook," the initials of his birthplace, Kinderhook, NY. Some claim that "orl korrect" was an intentional misspelling meant to show that supporters of Andrew Jackson, a close ally of Van Buren, could not spell.
I do hope that this helps! There are different variations on this story, though.
