Hellbilly music is a sub-genre of country music and can best be described as country's version of Heavy metal, a popular rock genre. It's basically country music, with elements of Heavy metal. Hellbilly music falls into the Alternative country genre, as it is not a mainstream country genre. Hellbilly music is also known as Metal-country, Metalbilly, and possibly many more names. David Alan Coe recorded a Hellbilly album called Rebel Meets Rebel. In the CD packaging, David Alan Coe makes the claim that it was him and the band members of Pantera that developed the fusion of country and metal, even though others get credit for it. (Garth Brooks and Metallica, according to Coe)
But whatever the origins, other Hellbilly artists include Hank Williams III.
The Hellbilly Sound
There is a wide variety of types of Hellbilly music. The genre should not be confused with Psychobilly, which is similar, but typically doesn't have metal influences, as it usually has elements of Punk rock rather than metal.
The Hellbilly sound makes use of a wide variety of both country and metal styles, on the country side of things, usually the traditional country music styles such as Honky tonk and Bluegrass music is used, while on the metal side of things there's often times elements of Death metal, Speed metal, Thrash metal and many others.