He was also called "Kozan ou" (king of mining industry) for bening a president of Kuhara Kogyosho (Hitachi copper mine), which later became Hitachi, Ltd. and Kuhara Zaibatsu.
日立製作所創立の基盤となった久原鉱業所（日立銅山）や久原財閥の総帥として「鉱山王」の異名を取った。