Grandpa Phil is Arnold Shortman's eccentric paternal grandfather and one of the longtime residents of the Sunset Arms boarding house. A former boxer with a colorful past, Phil is full of unusual stories, strange habits, and old-fashioned wisdom that often become part of Arnold's adventures. He shares a close bond with Arnold and his wife, Gertie, even though the two frequently bicker over their eccentric personalities. Phil's experiences and larger-than-life stories make him an important source of family history and comic relief in Hey Arnold!.