Joop ter Heul was a fictional character in a series of five books written for teenage girls by Dutch novelist Setske de Haan (1889-1948), who wrote under the pen name Cissy van Marxveldt. Joop was high-spirited, headstrong and stubborn. The first four books, published over a six-year period (1919-1925) deal with her high school years, her young adulthood, her marriage, and her sons. The last book was not written until more than 20 years later. The initial four books are best remembered today for being a very strong influence on diarist Anne Frank, both in the character of Joop, whom she identified with, and in the epistolary style in which the books were written, which she adapted for her own diary.