The History of Kakuro
Like Sudoku, Kakuro started life in an American puzzle magazine under a different name, and only became a household word decades later on the other side of the Pacific.
Cross Sums, Invented in America
The number-crossword puzzle now known as Kakuro was invented in 1966 by Jacques Cousin, a Canadian working for the puzzle publisher Dell Magazines, who introduced it in the United States under the name "Cross Sums" (also written "Cross Sum"). It quickly became a regular feature in Dell's puzzle magazines alongside Dell's other number and logic puzzles.
The idea combined the look of a crossword grid with arithmetic instead of vocabulary: black cells carrying clue numbers in place of crossword definitions, and white cells to fill in with digits whose sums had to match those clues.
A Japanese Name for a Second Life
Cross Sums crossed over to Japan, where the puzzle publisher Nikoli - the same company that would later popularize and name Sudoku - picked it up and gave it the name "Kakuro", a contraction of "kasan kurosu" (加算クロス), Japanese for "addition cross".
Through the 1980s, Kakuro grew into one of Nikoli's most popular puzzles in Japan, developing a following there well before the Sudoku boom that would later carry Nikoli's name to the rest of the world.
A Puzzle Rediscovered
Kakuro's international profile rose again in the mid-2000s in the wake of Sudoku's worldwide newspaper boom, as puzzle editors looking for a follow-up act turned to Nikoli's other number puzzles - introducing Kakuro to many Western solvers for the first time under its Japanese name, even though the puzzle itself had been invented decades earlier in North America.
That two-stage history is reflected in how the puzzle is still solved today: a Kakuro grid never needs guesswork, only the same run-by-run elimination Dell's original Cross Sums solvers used - simply expressed digit by digit, one clue at a time, the same principle this collection's generator uses in reverse to build a fresh puzzle out of a randomly filled grid.