Boris Weisfeiler (born 19 April 1941 – disappeared 4-5 January 1985) was a Soviet-born mathematician and professor at Penn State University who lived in the United States before disappearing in Chile in 1985. Declassified US documents suggest a Chilean army patrol seized Weisfeiler and took him to Colonia Dignidad, a secretive Germanic agricultural commune set up in Chile in the 1960s. The Chilean Pinochet military dictatorship alleged that he drowned. He is known for the Weisfeiler filtration, Weisfeiler–Leman algorithm, and Kac–Weisfeiler conjectures.