Maki Kaji was the creator of the popular numbers puzzle Sudoku. He died on August 10 at the age of 69 due to bile duct cancer. His Japanese company Nikoli announced the news of his death on Tuesday. 

He was known as the “Godfather of Sudoku”. Kaji created the puzzle to be easy for children and others who didn’t want to think too hard. He was born on October 8, 1951, in Sapporo, Japan. His father was an engineer at a telecom company and mother worked at a kimono shop.

The puzzle creator graduated from Shakujii High School in Tokyo and dropped out of Keio University.

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He is survived by his wife, Naomi, and two daughters.

Sudoku wasn’t until popular till 2004 and became a global hit, after a fan from New Zealand pitched it and got it published in the British newspaper The Times. Two years later, Japan rediscovered its own puzzle as a “gyakuyunyu,” or “reimport.”

He was chief executive at his puzzle company, Nikoli Co., which he founded with two two childhood friends in 1983. During his lifetime, he travelled to more than 30 countries spreading his enjoyment of puzzles.

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Every year, he held Sudoku championships and over 200 million people in 100 countries played the puzzle.

Sudoku was also never trademarked except within Japan, driving its overseas craze, Nikoli said.

“Kaji-san came up with the name Sudoku and was loved by puzzle fans from all over the world. We are grateful from the bottom of our hearts for the patronage you have shown throughout his life,” the company said in a statement.

Originally, Sudoku was called “Suji-wa-Dokushin-ni-Kagiru,” which translates to, “Numbers should be single, a bachelor.” In recent years, Sudoku, believed to be the world’s most popular pencil puzzle, has come out in digital versions.

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Yoshinao Anpuku, who succeeded Kaji as Nikoli’s chief executive, said Kaji made friends easily and had a “unique and playful approach toward life.”

“Our mission is to pursue Maki’s vision and possibilities,” Anpuku said.

Nikoli has provided original puzzles to more than 100 media companies, 10 of them foreign ones.

Major Japanese newspaper Mainichi in its obituary credited Kaji for starting the puzzle sections at bookstores, as well as introducing the word “Sudoku” into the Oxford English dictionary.

Kaji is survived by his wife Naomi and two daughters. Funeral services have been held among close family. A separate memorial service is being arranged by Nikoli, but details were still undecided.

“His most important contribution to the world of logic puzzles is subtle and underappreciated,” Nick Baxter, the captain of the US Puzzle Team, which competes in the World Sudoku Championship, wrote in an email.

In an interview with the BBC in 2007, Kaji said that the secret to inventing a good puzzle was to make the rules “simple and easy for everyone, including beginners.”