Grandpa Billy is Bob and Tom's grandfather. The only thing Bob has left of him is his tool box. He was a builder like Bob and Robert. He's probably dead because, Bob talked about him and kept his tool box. He was never seen.
Bob's tool box is really Grandpa Billy's. In culture, people would sometimes keep something to remember a dead family member.
- He seems to be the first character mentioned on the show to be deceased.