Frank Duncan is the father of Bob Duncan, ex-husband of Linda Duncan, and brother of Mel Duncan. In the episode, It's a Charlie Duncan Thanksgiving, he first appeared and fell in love with Mrs. Dabney, but when the Duncans left them alone for a hour, they had an argument and began to hate each other.
- He has two siblings: Mel Duncan and Stanley Duncan (Bob's two uncles).
- He is not married to Linda anymore.
- So far, he has only appeared in Good Luck Charlie once
- He is grouchy
- He hates cats
- He went out with Mrs Dabney
- Only he found out that he only liked her when other people were in the room
- His father is named Patrick John Duncan, the kids great-grandfather.