Harold Camping is a Christian minister who predicted the end of the world and the Rapture three times, unsuccessfully, but made a lot of money off of it. The first time was in 1994, the second was the famous May 21st, 2011 prediction, and the third was on October 21st, 2011. He said the world DID end after the May 21st prediction...spiritually, and that it wouldn't happen physically until the October prediction. He has made all these predictions by adding numbers in the Bible in an equation of some kind.
In March 2012, Camping and his ministry, Family Radio, posted a letter of apology for the incorrect predictions, adding that at least the campaign had the effect of making people more acquainted with the Bible.