The original Romanian birth certificate of his grandson, Rivin Altar ("Reuben") Kosviner, names Reuben's father as "Mr Altar sin Rivin", which translates as Altar son of Rivin. In those times Jews in Eastern Europe did not have proper surnames names, and used the format "[name] son of [father's name]", a format that is today used only in synagogues for prayer purposes. We don't know when he adopted the surname Kosviner, but from this we do know that his given name (or one of them) was Rivin.
