From Chinese 谷 (gǔ) referring to the ancient fief of Qin Gu, which existed in what is now the province of either Gansu or Shaanxi. Alternately it may come from the name of the fief of Jia Gu, which was part of the state of Qi during the Zhou dynasty.
From Chinese 古 (gǔ) possibly derived from Kucheng (古成 or 苦城), the name of an ancient fief that may have existed during the Zhou dynasty in what is now Henan province. Alternately it may come from the title Guguong (古公) meaning "old duke", which was given to 12th-century BC ruler King Tai of Zhou.