He was named Kinnosuke, to which the letter Kin was given for warding off evil fortune, because he was born on the day of Koshin (it was believed that a baby born on this day would grow up to be a master thief).
金之助という名前は、生まれた日が庚申庚申の日（この日生まれた赤子は大泥棒になるという迷信があった）だったので、厄除けの意味で「金」の文字が入れられた。