Though sudoku seemed to achieve ubiquity overnight in 2005, the puzzle has actually been around for decades. So-called magic squares were an occasional pastime among smarties during the days of Ben Franklin, who enjoyed the puzzles. Assigning absolute authorship for the modern version's invention is akin to crediting the wheel's designer, but several key people were integral to the creation of sudoku as we know and play it.

According to The New York Times, 18th-century Swiss mathematician Leonhard Euler studied conundrums called Latin squares, which involved plugging the same set of numbers into each row and column in a grid. Two hundred years after Euler, in 1979, retired American architect Howard Garns contributed puzzles titled Number Place for publication by Connecticut-based crossword giant Dell Magazines. Number Place added a key element to Latin squares, the nine boxes within the overall grid.

Enter Japanese publisher Nikoli Co., which in 1984 published Garns-style puzzles under the name sudoku. Pronounced "soo-DOH-koo," the word roughly translates as "only single numbers allowed." In 1997, Wayne Gould, a New Zealander and retired Hong Kong judge, was vacationing in Tokyo, where he stumbled across a sudoku book. It intrigued him and he developed a computer program to generate more of the puzzles.

When Gould was in London in October 2004, he dropped by The Times newspaper offices and convinced them to try publishing sudoku. Within weeks, the puzzles appeared in print, and readers were hooked. "I came across this puzzle that needed a lot of help and encouragement," Gould told Psychology Today, adding he is "the stepfather," not the father, of sudoku. Today, the puzzles appear in almost 400 newspapers in 60 countries.

An assortment of interesting sudoku factoids.

• "Su doku" stems from the Japanese words "su," meaning "number," and "doku," or "single."

• "The craze, judging by history, will last four, five, six months, and then it will taper off," The New York Times crossword editor Will Shortz told Fortune in October 2005. By the May/June 2006 issue of Psychology Today, Shortz allowed that sudoku had the staying power of crosswords.

• There are 6,670,903,752,021,072,936,960 possible combinations for completing a 9-by-9 sudoku grid.

• In Japan, the puzzles are called by their English name, Number Place; in English publications, the puzzles go by their Japanese name, sudoku. Go figure.

• British Airways forbids its flight attendants from puzzling over sudoku during takeoff and landing. (Source: The New York Times, 05/06/06)