First of all, the word ancestor has its own meaning. There are many pictographs in ancient Chinese characters, which are characters evolved from graphics. In Oracle Bone Inscriptions, there is only one word "He" on the right, which looks like a memorial tablet, and here, it means memorial tablet.
Ancestors include: my father's name is father, ancestor. Father's father is called grandfather, the second ancestor. Grandfather's father is called great grandfather, the third ancestor. Great-grandfather's father's name is Gaozu, Sizu. Gaozu's father is called Tianzu and Wuzu. Tianzu's father is called Zu, the sixth ancestor. Liezu's father is called Taizu, the seventh ancestor. Taizu's father is called Yuanzu, the eighth ancestor. Yuanzu's father is called the first ancestor and the ninth ancestor, which is what we often call the first ancestor.