Today in 1839, the expression "OK" was first used in print. It appeared in Boston Morning Post article about the Anti-Bell-Ringing Society. From Smithsonian (image: OK Krew 509):
Ever since, scholars have passionately and voluminously debated the etymology of the expression. Most likely it grew out of a fad in the 1830s, for comical misspellings and initialisms. One of those misspellings was "Oll Korrect.""March 23, 1839: OK, OK, Already"