Beginning of the Family
The man in question was named Martin Fugate. He fell in love with and married a local Kentuckyian, Elizabeth Smith, and had children. After a while, their children and other descendants went on to marry more local folks. A lot of the time, their bloodlines were terribly close together, which is grounds for mutations. Since Hazard was such a remote and isolated town, it only made sense for this type of interfamily marriages to happen.