Willem Rutger van Zwet (31 March 1934 – 2 July 2020) was a Dutch mathematical statistician.^[2] He was a professor at Leiden University between 1968 and 1999.

Van Zwet was born on 31 March 1934 in Leiden.^[3] Van Zwet obtained his doctoral degree in 1964 under the supervision of Jan Hemelrijk at the University of Amsterdam with a thesis titled "Convex Transformations of Random Variables".^[4] After that, he worked at the Centrum Wiskunde & Informatica in Amsterdam, and became a lector of statistics at Leiden University in 1964 and was named professor in 1968. He retired in 1999.^[3]

From 1992 to 1999, van Zwet was the Director of the Thomas Stieltjes Institute of Mathematics. He co-founded Eurandom in 1997, and served as its director until 2000. From 1997 to 1999, he was also the President of the International Statistical Institute.

Van Zwet was a Fellow of the Institute of Mathematical Statistics and a member of the Academia Europaea since 1990.^[5] He received the Humboldt Prize in 2006. He won the Adolphe Quetelet Medal in 1993, and had been a Fellow of the Royal Statistical Society since 1978. In 1979, he became a member of the Royal Netherlands Academy of Arts and Sciences.^[6] In 1996, he was made Knight of the Order of the Netherlands Lion, and was named Doctoris Honoris causa of Charles University the following year. He died on 2 July 2020 in Oegstgeest.^[3]