Willem de Ridder (14 October 1939[3] – 29 December 2022) was a Dutch anarchist[4] and artist, known as a founder of Fluxus.[5] He was the foremost Fluxus member in the Netherlands. He showed and sold Fluxus works in his gallery, Amstel 47, and shops Fluxshop and European Mail-Order Warehouse. He organized Dutch Fluxus festivals with Wim T. Schippers in 1963 and 1964.[3]
De Ridder's Amsterdam club, Provadya, was a center for the city's counterculture.[6]
He graduated from the Academy of Arts in Den Bosch. After finishing his studies, he decided to stop painting.[7]