On August 21, 2004, Jeffy was born to Nancy and Jacques Pierre François in a porta potty on 7 Jeffy Street in Paris, France. At one point, along with Nancy and presumably Jacques, Jeffy moved to Pensacola, Florida in the United States. He was constantly abused by Nancy for no apparent reason.
Jeffy first appears in Mario The Babysitter after Mario wakes up and had a kid dropped off at his house named Jeffy.