The Cool grandfather is an unnamed father of Mav or Portia.


When the Simpson family visited Mav's and Portia's house, they met the cool grandfather there. He said that he loved "shutting up and giving away money" and gave some money to Homer. He also mentioned that he wore "promise stone" which meant that if he was ever a burden, he would jump into the volcano.Then so The Cool Grandfather is not later seen.