Who is grandfather in Chains?

Grandfather is a fairly minor character in this book. He is the old man who works the Tea Water Pump, and Curzon calls him "grandfather" when he is there with Isabel in chapter 13. Isabel mistakenly thinks that the relationship is real, but then she learns that a lot of people refer to him as "grandfather." This is because he is one of the oldest slaves in the area. He is described as a man "with stone-gray hair and skin the color of the night sky." Isabel feels an immediate kinship with the old man because he has a scar that reminds her of her own father.
Despite being a minor character, he does play a vital role in the story. It is his advice that provides Isabel with a catalyst that propels her into action in order to secure her own freedom from the Locktons and slavery.

You must choose your own side, find your road through the valley of darkness that will lead you to the river Jordan . . . Everything that stands between you and freedom is the river Jordan