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In a notice posted on Monday, August 16, his publicist said Maki Kaji died at home on August 10 after battling cancer.

Japanese publisher, popularly known as the "father of Sudoku", Maki Kaji has lost the battle to cancer at 69.

In a notice posted Monday, August 16, Nikoli said Maki Kaji died at home on August 10 after battling cancer, and a memorial service would be held at a later date.

"Mr Kaji was known as the father of Sudoku and was loved by puzzle fans all around the world," the publisher said in a statement on its website.

Kaji was a university dropout who worked in a printing company before founding Japan’s first puzzle magazine. He took hints from an existing number puzzle to create what he later named "sudoku".

Sudoku, a sort of numerical crossword, was invented by Swiss mathematician Leonhard Euler in the 18th century.

The modern version is sometimes said to have been formulated in the United States, but Kaji is credited with having popularised the puzzle.

He is also said to have come up with the name Sudoku, a contraction of a Japanese phrase meaning "each number must be single".

The puzzle challenges people to fill a grid of 9x9 blocks, with nine boxes in each block so that all columns, both vertical and horizontal, contain the numbers one to nine without repetition. The number of filled-in figures for a grid at the start of the puzzle determines how difficult it is.

Sudoku became popular outside Japan around two decades ago after overseas newspapers began printing the puzzles. It is now praised as a way to keep mental faculties sharp, with more than 100 million people around the world estimated to try the puzzles regularly.

A world championship has been held annually since 2006.

Kaji continued to create and refine puzzles with the help of readers of his quarterly puzzle magazine. He stepped down as head of his company in July 2021 due to ill health and died from bile duct cancer on 10 August.