The Father, the Son, and the Holy Fonz is episode 18 of family guy season 04. It was originally aired on December 18, 2005.
When Peter’s dad visits the Griffins, he tries to impose his religious beliefs on the family. But after a mishap leaves Stewie stuck living in a bubble, Peter searches for a new religion finding faith in his television hero the Fonz. But “Happy Days” are not quite here as the newly established Church of the Fonz struggles to retain its members.