Maki Kaji, a university dropout, worked in a printing company before founding Japan’s first puzzle magazine. As a puzzle enthusiast, he created sudoku by using an existing number puzzle sometime in the mid-80s. Kaji was credited for turning the number puzzle into a worldwide phenomenon.

Sudoku is a logic-based, combinatorial number-placement puzzle. In classic sudoku, the objective is to fill a 9×9 grid with digits so that each column, each row, and each of the nine 3×3 sub grids that compose the grid contains all of the digits from 1 to 9. French newspapers featured variations of the Sudoku puzzles in the 19th century, and the puzzle has appeared since 1979 in puzzle books under the name Number Place. However, the modern Sudoku only began to gain widespread popularity in 1986 when it was published by Kaji’s company, Nikoli under the name Sudoku, meaning “single number”.

In the company’s website, it wrote “Known as the Godfather of Sudoku, he (Maki Kaji) was adorned by puzzle lovers around the world and we would like to express our gratitude to all of you”. Kaji had continued to create puzzles with help from his readers until he stepped down as head of his company due to ill health. He died on 10 August after losing his battle to cancer at age 69.

In an interview with BBC in 2007, Kaji said that the secret to inventing an excellent puzzle was to keep the rules simple. “I get really moved when I see a new idea for a puzzle which has lots of potential. It is like finding treasure. It’s not about whether it will make money, it is purely the excitement of trying to solve it.”