Where Did "OK" Come From?

How did two little letters end up becoming one of the most common words used in the English language?

OK, how did two little letters become one of the most common words used in the English language? It’s OK if you don’t have any idea because the supposed origins of the word are as varied as the many ways in which it is used.

OK, or okay, they’re both OK, means everything is all right, just dandy. “Are you having a heart attack?” “No, I just ate a spicy b…