Marjorie "Marge" Dursley is Vernon Dursley's sister. She breeds dogs (12 of them), does not like Harry, and the feeling is quite mutual. When she visits, she always brings expensive gifts for Dudley, but once brought dog biscuits as a gift for Harry.
During the summer of 1993, she stayed at the Dursleys' house for a week, belittling Harry all the time. When she finally went too far (insulting his parents), Harry lost control of his magic, inflating her like a balloon and floating her to the ceiling. She had her memory modified by the Accidental Magic Reversal Squad of the Ministry of Magic.