Maki Kaji (鍜治 真起, Kaji Maki, 8 October 1951 – 10 August 2021^[1]) was a Japanese businessman who was the president of Nikoli, a puzzle manufacturer. He is widely known as "the father of Sudoku" for his role in popularizing the number game.^[2][3]

Kaji was born in Sapporo on 8 October 1951.^[4][5] His father worked as an engineer at a telecom company; his mother was employed by a kimono shop. Kaji attended Shakujii High School in his hometown. He later studied literature at Keio University, but dropped out during his first year.^[4][6] After a succession of jobs including being a roadie, a waiter and a construction worker, he started a publishing business.^[6]

Kaji launched a quarterly puzzle magazine in 1980 called Nikoli,^[7] together with two friends from his childhood.^[4] They named the magazine after a race horse that had won the 1980 2000 Guineas Stakes race in Ireland.^[6][8] Three years later, he founded a company under the same name.^[5] The magazine, the company's main product, grew to have 50,000 quarterly readers.^[9]

The number game Sudoku appeared in early issues of Nikoli.^[7] He formulated the name "Sudoku" while he was scrambling to get to a horse race.^[4][10] He shortened it from Suuji wa dokushin ni kagiru ("numbers should be single") at the urging of his fellow workers.^[10] After the game spread to Britain^[11][12] and the United States,^[8] it became wildly popular.^[7]

Kaji also invented or introduced various other puzzle games, such as Masyu.^[9] He resigned as head of Nikoli on 31 July 2021,^[13] ten days before his death.^[4][14] He was succeeded as president by Nikoli's editor in chief, Yoshinao Anpuku.^[13]

Kaji was married to Naomi until his death. Together, they had two children.^[4]

Kaji died on 10 August 2021 at his home in Tokyo at age 69, from bile duct cancer.^[4][15] Nikoli's staff held a memorial gathering for him on 2 November in Tokyo.^[16]