The term "Plumber's grandfather" is conjectural. This article's real name is unknown and a non-canonical nickname or title is used instead. Please see the reasons for this title in the "Behind the scenes" section below, and/or the relevant discussion on the talk page.
The Plumber's grandfather was a character mentioned in Ratchet & Clank. The Plumber's grandfather was the inventor of the Metal Detector and was referred to as a "cheap old man" for how he used it.