Hartog Zak was a son of Machiel Zak and Judith Olivier. He married 17 November 1897 in Amsterdam to Esther de Jong, a daughter of Abraham de Jong and Dina Waterman.
Hartog himself was born in a family with twelve children. Two of them died in childhood. The other children were all killed during the Holocaust.
City Archive of Amsterdam, family registration card of Machiel Zak, archive card of Hartog Zak and website www.wiewaswie.nl.