The oldest known member of the Mulder family, Fox's grandfather was deceased by 1995 but was alive during Fox's childhood. He was known to have a poor stomach (TXF: "The Căluşari"), and also for slurping up his soup. (TXF: "Theef") It is possible that Fox was speaking of two separate grandfathers in those separate incidents. It is also possible that he was speaking sarcastically and making up those events. It was never established if either grandfather was William's father, a Mulder, or Teena's father, a Kuipers.