Origin of the term OK or 'okay'

Could someone please tell me the derivation of this term?
Despite asking lots of people over lots of years this question has never been answered to my satisfaction.

I asked my Mum whether it was one of the wartime GI acronyms (SNAFU etc). All she could say was she thought it was in use prior to WW2.

I feel I am going to regret asking this but…
Has anyone any idea,please?

The answer, according to Cecil, is: “The letters, not to keep you guessing, stand for ‘oll korrect.’ They’re the result of a fad for comical abbreviations that flourished in the late 1830s and 1840s.”

Cecil’s full report appears in What does “OK” stand for?, from his second opus, More of the Straight Dope.

Thanks for the answer & link. That is by far the most comprehensive & authorative reply I have received.