Willem Postma, born in Harlingen on April 20, 1898, son of Johannes Postma (bricklayer) and Grietje Bouwmeester, coppersmith.

Willem was married in Harlingen on September 5, 1927, at the age of 29 to
Wiepkje de Groot (aged 24 years), born in Harlingen on April 10, 1903, daughter of Tjerk de Groot and Anna Kwast.