Mr Potter was the husband of Mrs Potter and the father of James Potter I. By consequence, he was the paternal grandfather of Harry Potter. Mr Potter went to Hogwarts School of Witchcraft and Wizardry, where he was sorted into Gryffindor House.
When Sirius Black ran away from home at age sixteen, Mr and Mrs Potter invited him to stay at their home during the holidays, and adopted him as a second son. When he got a place of his own the following year, they ensured he came back for tea every Sunday.
By October 1981, Mr and Mrs Potter had died; their orphaned grandson Harry, whose parents had been slaughtered by Lord Voldemort, was sent to live with his only living relatives, Vernon and Petunia Dursley.