It's "OK"

The term “O.K.” was popularized by Martin Van Buren. Van Buren was from Kinderhook, New York, sometimes referred to as Old Kinderhook in speeches and print. When he signed off on documents, he found it easier to initial things with “O.K.” instead of his full Dutch name. Eventually, “O.K.” and the spelled out version, “okay” came to mean “all right”.