Ruben Kalker was a son of Nathan Kalke and Eva Walg, a family with nine children: Zaartje, Lientje, Rijntje, Salomon, Gabriel Salomon Herman, Minetta and Simon Hartog. He married in Heerjansdam on 25 March 1891to Elizabeth den Hartog.
Municipal Archive of Rotterdam, Civil Registry - family registration card of Ruben Kalker and website www.wiewaswie.nl and the Regional Archive of Tilburg, register of births of Geertruidenberg.
Ruben Kalker was a witness in 1918 at the marriage of Hendrik Polak and Hester Beerenborg in The Hague. At that time he was the director of an orphanage in Rotterdam.
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