Grandfather Bolte is Georgie and Agatha's grandfather and Ma's father. The truth is, though, he gets along with Georgie best of all. They value the same things—namely, the general store and guns that shoot straight. Grandfather Bolte is a businessman. He invests heavily in supplies for pigeoners and cleans up when the pigeons nest five miles from Placid.
However, this keen business sense is where he and Agatha misunderstand each other, though: He thinks the purpose of college is to get a husband, which she can do for free right in Placid. He sees only the return on investment aspect of higher education, and he's super practical. Georgie says Grandfather Bolte "had a body like steel on hinges: strong, functional, but rather mechanical. I don't mean any disrespect, but my grandfather's body was about as interesting as a printing press, a butter churn, or a clothes-washing wringer" (5.88). Yup—practical to his core.
Grandfather Bolte's funeral bookends Agatha's at the beginning of the book. In an interesting twist, his death actually saves Billy's and Georgie's lives because his death is the reason Mr. Olmstead comes to find them. His death is unexpected and sudden, but the preparation Georgie has undergone with Agatha's fake death equips her to cope with a real death in her family. In the end, Georgie doesn't lose Agatha, but she does lose Grandfather Bolte, so all that time she spends learning to accept death isn't wasted.