Colonel Fubster was a Muggle man who was a neighbour of Marjorie Dursley. After his retirement from the British Armed Forces, he apparently spent a lot of time with her, and was willing to do her favours. He watched over her dogs when she went to visit her brother and his family in the summer of 1993 (excepting Ripper, who Marge took along on the trip, as she said he couldn't stand to be parted from her).
The year before, he drowned one of Marge's pups at her request, as she considered it a "weak," "underbred", "ratty little thing." Marge also claimed to have accidentally shattered a wine glass on a visit to the Colonel's house the day before she left to visit her brother.
Marge is secretly in love with him, but he will never marry her, due to her truly horrible personality.