Picture 15
Gender Male
Family Dextamina (sister)
Dexter (grandson)
Dee Dee (granddaughter)
Dad (son-in-law)
Mom (daughter)
Fergle O'Reilly (son)
Unnamed daughter
First Appearance The Grand-Daddy of All Inventions

Grandpa is Dexter and Dee Dee's maternal grandfather and Dextamina's younger brother.


Just like his grandson Dexter, he also has laboratory, as shown in The Grand Daddy of All Inventions. However unlike Dexter's massive and high tech lab, his was a small space in his garage. Grandpa is also implied to be smarter than Dexter since, with a relatively simple set up he was able to create a self sustaining power source, which Dexter failed to do with his complex machinery.

Episode Appearances


  • He is Mom's father since Mom refers him as "Dad".
  • His design is identical to Dexter's future self, Old Man Dexter, indicating that Dexter inherits both his looks and genius from his grandfather.
  • His only official appearance was in the episode The Grand Daddy of All Inventions however, he was mentioned in the episode Old Man Dexter.