Donald J. Sobol, the author of the extremely popular boy-detective book series 'Encyclopedia Brown,' died last week of natural causes. He was 87.

If you were born after 1960, you've likely read at least one of the almost 30-book strong franchise, which follows the mystery-solving adventures of the 10-year-old Brown and his tomboy sidekick Sally Kimball.

While 'Encyclopedia Brown' has never gone out of print since debuting in 1963, Sobol was met with skepticism when he first pitched the idea to publishing houses. In fact, Sobol, who turned to fiction after a successful career in journalism, had his first 'Brown' manuscript rejected 24 times before finally finding a taker.

When it was published, the characters became an almost instant sensation with school children everywhere. Despite the success of his book, Sobol tried to remain as anonymous as possible and had a long-standing policy against television interviews or even being photographed.

"I am very content with staying in the background and letting the books do the talking," he told an Oberlin alumni magazine last year.

The 'Encyclopedia Brown' series has been translated into 12 languages and has spawned both a daily comic strip, which ran from 1978 to 1980, and an HBO series, which aired in 1989.

Celebrate the life of Sobol with some classic 'Encyclopedia Brown' covers and videos below.

HBO's 'Encyclopedia Brown' TV series

Funny, NSFW 'Encyclopedia Brown' Parody

NSFW 'Mystery Team' Trailer (inspired by 'Encyclopedia Brown')