OK started as a joke nobody expected to last
It was misspelled on purpose, printed once as filler, and should have died within the week. It didn't.
On March 23, 1839, an editor at the Boston Morning Post named Charles Gordon Greene printed "o.k." in a satirical item, glossing it as "oll korrect." This was not an isolated stroke of genius. Boston newspapers in the 1830s were in the grip of a fad for deliberately misspelled abbreviations — the same energy as today's "NBD" or "IYKYK" — and most of them, like "OW" for "oll wright" and "KG" for a mangled "no go," vanished within months.
OK should have gone the same way. What saved it was an accident of timing: in the 1840 presidential race, Martin Van Buren's nickname was Old Kinderhook, and his campaign realized the initials matched. "Vote for OK" clubs sprang up nationwide. Van Buren lost the election. OK won it anyway — it stuck in the language, got adopted by the telegraph as a quick signal that a message had come through clean, and eventually spread into languages that don't even use the Latin alphabet.
Merriam-Webster now calls it, very probably, the most widely recognized word on the planet.
Someone in a 19th-century newsroom made a throwaway joke about spelling and accidentally out-lived every serious word he ever wrote.