Rien Poortvliet (August 7, 1932 – September 15, 1995) was a Dutch draughtsman and painter.

Born in Schiedam, he was best known for his drawings of animals and for "Gnomes" in the famous series of books published by Harry N. Abrams, Inc. of New York City.

Being a plasterer's son from Schiedam, making a living as an artist did not seem an option for Rien Poortvliet. His parents were strict Dutch Reformed and were opposed to the idea of their oldest son going to an art academy.

Rien's aptitude for drawing showed early on. After primary education the young Rien worked at an ad agency, where he could make some use of his talent. He unmistakably also had talent for the advertising profession, because after he had completed his draft time in the Navy he rose to senior manager at Lintas, Unilever's ad agency.

Yet Rien took more pleasure in the work he did on the side for several publishers. He illustrated various books, among them works by Jaap ter Haar, Leonard Roggeveen and Godfried Bomans. He was also a passionate hunter, which led him to drawing various nature subjects.

At the end of the 1960s Poortvliet had made it to where he could resign as a publisher and start as an independent illustrator. However, he did not have enough work, so to earn enough to make a living he made a book out of his drawings and watercolours based on his hunting experiences. Later on, he also made a similar work concerning the life of Jesus Christ.

Poortvliet saw himself as a characteristic narrator. His drawings told the tale, at most he added a short caption.

For years his works were published by Van Holkema en Warendorf in Bussum, where his "Leven en werken van de Kabouter" (co-authored by Wil Huygen, English title is "Gnomes") saw an astonishing 59 printings. With the Gnomes series Poortvliet acquired international fame. While he was alive, but more so after his death this series took on a life of its own, and was turned into an animated series.

His books were translated into English, French, German, Swedish, Finnish, Italian and other languages.