Asa Phelps was a member of the Flying Hellfish, Grampa's unit in World War II. Along with the rest of the unit, he took part in a tontine where the last surviving member would take sole possession of a group of paintings they liberated. He was the seventh member of the group to die.
According to Reverend Lovejoy's ephiny, Asa was in Springfield for all of his life, save for when he served in World War II as a member of the Flying Hellfish and during a day trip in High School. He also worked at the United Strut and Bracing Works as a molder. However he was replaced by a Molder-Matic, and it's implied that he committed suicide as a result.