A university dropout who worked in a printing company before founding Japan’s first puzzle magazine, Kaji took hints from an existing number puzzle to create what he later named “sudoku” – a contraction of the Japanese for “every number must be single” – sometime in the mid-80s.
“Known as the Godfather of Sudoku, he was adored by puzzle lovers around the world and we would like to express our gratitude to all of you,” his company, Nikoli, said on its website on Monday.
Kaji died from bile duct cancer.
Sudoku became popular outside Japan about 20 years ago after overseas newspapers began printing it. Praised as a way to keep mental faculties sharp, more than 100 million people around the world are estimated to try the puzzles regularly. A world championship has been held annually since 2006.
“I get really moved when I see a new idea for a puzzle which has lots of potential,” he told the BBC in 2007, adding that the secret to inventing a good puzzle was to make the rules simple.
“It is like finding treasure. It’s not about whether it will make money, it is purely the excitement of trying to solve it.”