"Pop-Pop" Griffin is Peter's grandfather or great-grandfather.

After Peter and the guys stand up to the police and demolition crew long enough for Jerome to purchase The Drunken Clam in "Save the Clam", Peter proudly notes that he believed in himself just as his Pop-Pop always said. However, as Pop-Pop appears in Peter's thoughts, his real words are to ask for rat poison to simply die which Peter denies him, brushing it aside to note that they did it together.