Comes from 4chan slag. It's the opposite of cucked. Hence the term `based and redpilled` to `cringe and bluepilled`. It's also typically used to endorse extreme views ironically: "beating women is based" or endorsement to strange ideas "monarchism is based". A discussion above mentions some rapped coining the word, but often words occur spontaneously in multiple communities and both can claim invention of a term.

Thanks! I'm getting old.