When the 100 TV series premiered on March 19, 2014, The CW instantly knew they had hit the jackpot. It was a resounding success.

The series went on to have—appropriately enough—a hundred episodes divided into seven seasons, all of which received a warm critical reception and high ratings that remained somewhat stable throughout its run.

But with the popularity of the TV series, it can be easy to forget it was originally a New York Times best-selling book series penned by Kass Morgan.