Concept:Maki Kaji was best known for popularising Sudoku, a logic-based number puzzle.
Explanation:Maki Kaji was a Japanese businessman who served as the president of Nikoli, a puzzle manufacturing company.
He did not invent the original number puzzle, but he transformed it into the familiar 9x9 grid format and named it Sudoku.
His company, Nikoli, published and promoted the puzzle in Japan, from where it spread across the world.
Because of his immense contribution, he was popularly known as "the father of Sudoku."
The other options, such as lithium-ion battery, abacus, and cassette-tape player, are unrelated to his work in puzzles.
Therefore, his recent death reminded people of his lasting legacy in the world of puzzle games.
Answer:Option C. Sudoku.