Bathory

Bathory is a very interesting band. It is actually a single composer who makes his songs entirely on his own. 

Many of his songs have very unique sound. They are not just metal heavy, but they are also very eerie and mysterious. For example, Enter the Eternal Fire or Call from the Grave. Listening to these songs can let you easily imagine satanic cultists, summoning demons in dark rituals. 

Hades has more traditional and dynamic metal sound instead. It still has some mysterious feel to it.