Martin Gardner started his 25 year career of writing mathematical recreation articles for Scientific American in December 1956.  Some of the topics he helped introduce to the general public included hexaflexagons (specially folded hexagons), rep-tiles (multiple identical polygons put together to reproduce a larger version of themselves), and the Soma cube (which is a 3x3x3 cube made of 7 smaller sets of cubes).

Gardner has also authored several books on mathematical recreation including The Unexpecting Hanging & other Mathematical Diversions, aha! Insight, and aha! Gotcha.  The Unexpected Hanging is a popular paradox that appears in various forms.  The basis is that a person is told that they will be hung sometime in the next week, but the actual day will be a surprise.  The person who is about to be hung starts by reasoning that they cannot be hung on the last day of the week, because if the person was not hung by the end of the sixth day, the only day left to be hung is the seventh and therefore no longer a surprise.  However, by similar reasoning the person realizes that the hanging cannot occur on the second to last day of the week since they would believe that the hanging would occur on that day since it cannot occur on the last day.  Therefore it would no longer be a surprise to be hung on that day either. The reasoning follows all the way back to the first day of the week leaving the paradox that the surprise hanging can never occur.

Author: Eric Libicki

References:
http://www.geocities.com/CapeCanaveral/Hangar/2643/gardner.htm

Gardner, Martin. "A Quarter-Century of Recreational Mathematics".
Scientific American. August 1998 68-75.