Willem Muijs was the youngest son of Samuel Muijs and Sara Stokvisch. He was born on 16 November 1915 in Amsterdam and he started his working life as a butcher's assistant. On 8 June 1938 he married Hendrika Smeer in Amsterdam, a daughter of Salomon Smeer and Marietje Roeg.
From July 1937, Willem no longer lived at home but found a place to live with "uncle" Levie Rijksman at Rapenburgerstraat 58…